Agilent_7890A_Troubleshooting

Agilent_7890A_Troubleshooting
Agilent 7890A
Gas Chromatograph
Troubleshooting
Agilent Technologies
Notices
© Agilent Technologies, Inc. 2011
Warranty
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Manual Part Number
G3430-90017
Edition
Sixth edition, July 2011
Fifth edition, June 2010
Fourth edition, January 2010
Third edition, April 2009
Second edition, May 2008
First edition, March 2007
Printed in USA
Agilent Technologies, Inc.
2850 Centerville Road
Wilmington, DE 19808-1610 USA
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Safety Notices
CAUTION
A CAUTION notice denotes a hazard. It
calls attention to an operating
procedure, practice, or the like that, if
not correctly performed or adhered to,
could result in damage to the product
or loss of important data. Do not
proceed beyond a CAUTION notice
until the indicated conditions are fully
understood and met.
WA R N I N G
A WARNING notice denotes a hazard.
It calls attention to an operating
procedure, practice, or the like that, if
not correctly performed or adhered to,
could result in personal injury or
death. Do not proceed beyond a
WARNING notice until the indicated
conditions are fully understood and
met.
Contents
1
Concepts and General Tasks
Concepts 10
How to troubleshoot using this manual
The [Status] key 10
Error conditions 10
10
Configurable Items to Always Keep Current
Inlet and detector configuration 11
Column configuration 11
Automatic Liquid Sampler configuration
Gas configuration 11
11
11
To View the Run Log, Maintenance Log, and Event Log
Run Log 13
Maintenance Log 13
Event Log 13
Information to Obtain Before Calling Agilent for Service
2
14
ALS and Detector Symptoms
Plunger Errors
Procedure
16
16
Vial Mishandled by ALS (7693A)
17
Alignment Light on 7693A Injector Tower is On
Vial Mishandled by ALS (7683)
Syringe Needle Bends During Injection into Inlet
FID Fails Leakage Current Test
Possible causes 24
Procedure 24
NPD Fails Leakage Current Test
FID Fails Baseline Test
19
20
Alignment Light on 7683B Injector Tower is On
22
23
24
25
26
To Resolve Low Sensitivity with an FID
Troubleshooting
13
27
3
FID Does Not Ignite
28
FID Ignitor Does Not Glow During Ignition Sequence
Corrosion in FID Collector and Ignitor Glow Plug
FPD Does Not Ignite
31
32
NPD Adjust Offset Process Fails
NPD Bead Will Not Ignite
34
35
Shutdown (Defective) Device
3
29
36
Chromatographic Symptoms
Retention Times Not Repeatable
Peak Areas Not Repeatable
38
39
Contamination or Carryover 40
Isolate the source 40
Check possible causes—all inlet and detector combinations
Larger Peaks Than Expected
Peaks Not Displayed/No Peaks
43
44
Baseline Rise During Oven Temperature Program
Poor Peak Resolution
Peak Tailing 48
NPD Peak Tailing
40
46
47
49
Peak Boiling Point or Molecular Weight Discrimination Poor 50
For any inlet operating in split mode with any detector 50
For any inlet operating in splitless mode with any detector 50
Sample Decomposition in Inlet/Missing Peaks
Peak Fronting
51
52
Noisy Detector, Including Wander, Drift, and Baseline Spikes
Noisy baseline 53
Baseline wander and drift 55
Baseline spiking 56
53
Microcell Electron Capture Detector (uECD) Noise and Sensitivity
Display signal evaluation 60
Sensitivity 61
Contamination (high baseline) 62
Low Peak Area or Height (Low Sensitivity)
To Resolve Low Sensitivity with an FID
63
64
FID Flame Goes Out During a Run and Attempts to Reignite
4
59
66
Troubleshooting
FID Baseline Output Above 20 pA
68
FID Baseline Output at Maximum (~8 Million)
69
FPD Flame Goes Out During a Run and Attempts to Reignite
FPD Quenching/Repeatability
71
FPD Output Too High or Too Low
FPD Low Peak Areas
72
73
FPD Large Peak Width at Half-Height
FPD Baseline Output High, > 20 pA
74
75
FPD Chromatographic Output Showing Clipped Peaks
NPD Solvent Quenching
NPD Response Low
76
77
78
NPD Baseline Output > 8 million
80
NPD Adjust Offset Process Not Functioning Properly
NPD Low Selectivity
70
81
82
Negative Peaks Seen with TCD
83
TCD Baseline Has Dampened Sinusoidal Noise Trailing Peaks (Ringing
Baseline) 84
TCD Peaks Have Negative Dip on Tail
4
85
GC Not Ready Symptoms
GC Never Becomes Ready
88
Flow Never Becomes Ready
89
Oven Temperature Never Cools Down/Cools Very Slowly
Oven Never Heats Up
90
91
Temperature Never Becomes Ready
Cannot Set a Flow or Pressure
92
93
A Gas Does Not Reach Setpoint Pressure or Flow
A Gas Exceeds Pressure Setpoint or Flow
The Inlet Pressure or Flow Fluctuates
94
95
96
Cannot Maintain a Pressure as Low as the Setpoint on a Split Inlet
The Measured Column Flow Does Not Equal the Displayed Flow
FID Does Not Ignite
98
99
FID Ignitor Does Not Glow During Injection Sequence
Troubleshooting
97
100
5
FID or NPD Measured Hydrogen and Makeup Gas Flows Much Less Than
Setpoint 102
NPD Adjust Offset Process Fails
FPD Does Not Ignite
103
104
Valve Not Ready 106
External valves
106
Gas sampling valves 106
Multiposition valve 106
5
Shutdown Symptoms
Column Shutdowns
108
Hydrogen Shutdowns
Thermal Shutdowns
6
110
112
GC Power On and Communication Symptoms
GC Does Not Turn On
114
PC Cannot Communicate with GC
115
GC Does Not Recover After Firmware Update
116
GC Turns On, Then Stops During Startup (During Self-Test)
7
117
Checking for Leaks
Leak Check Tips
120
To Check for External Leaks
To Check for GC Leaks
121
123
Leaks in Capillary Flow Fittings
124
To Perform an Inlet Leak Check 125
To set warning limits for a leak check 127
To disable a warning limit for the inlet leak check
127
To Check for Leaks in a Split/Splitless Inlet 128
Cannot Reach Pressure Setpoint 128
Low Sensitivity or Poor Repeatability 129
To Perform a SS Pressure Decay Leak Test
130
To Check for Leaks in a Multimode Inlet 131
Cannot Reach Pressure Setpoint 131
Low Sensitivity or Poor Repeatability 132
To Perform a MMI Pressure Decay Test
To Perform a PP Pressure Decay Leak Test
6
133
134
Troubleshooting
To Perform a COC Pressure Decay Leak Test
To Perform a PTV Pressure Decay Test
To Perform a VI Pressure Decay Test
8
135
136
137
Troubleshooting Tasks
To Measure a Column Flow 140
Measuring FID, TCD, uECD, and FPD column flow
Measuring NPD column flow 142
To Measure a Split Vent or Septum Purge Flow
To Measure a Detector Flow 146
Measuring FID, TCD, uECD, and FPD flows
Measuring NPD flows 148
To Perform the GC Self-Test
140
144
146
151
To Check or Monitor Split Vent Line Backpressure 152
To set a warning limit for the inlet trap check 153
To disable a warning limit for the inlet trap check 154
To Run the Inlet Trap Check
155
To Perform a SS Split Vent Restriction Test
To Adjust the FID Lit Offset
157
158
To Verify That the FID Flame Is Lit
159
To Verify FID Ignitor Function During Ignition Sequence
To Measure FID Leakage Current
161
To Measure FID Baseline Output
162
To Isolate the Cause of FID Noise
163
To Measure NPD Leakage Current
To Check for a Plugged FID Jet
164
165
To Check for a Plugged NPD Jet
166
To Verify That the NPD Bead Is Ignited
To Verify That the FPD Flame Is Lit
To Adjust the FPD Lit Offset
When to Change Gas Purifiers
167
168
169
170
To Check a Split Vent Line for Contamination
To Ignore a Device’s Readiness State
Troubleshooting
160
171
173
7
8
Troubleshooting
Agilent 7890A Gas Chromatograph
Troubleshooting
1
Concepts and General Tasks
Concepts 10
Configurable Items to Always Keep Current 11
To View the Run Log, Maintenance Log, and Event Log 13
Information to Obtain Before Calling Agilent for Service 14
Agilent Technologies
9
1
Concepts and General Tasks
Concepts
This manual provides lists of symptoms and corresponding
tasks to perform should you experience errors associated
with GC hardware or chromatographic output, GC Not Ready
messages, and other common issues.
Each section describes a problem and provides a bulleted list
of possible causes for you to troubleshoot. These lists are not
intended for use in the development of new methods.
Proceed with troubleshooting under the assumption that
method(s) are working properly.
This manual also includes common troubleshooting tasks as
well as information needed prior to calling Agilent for
service.
How to troubleshoot using this manual
Use the following steps as a general approach to
troubleshooting:
1 Observe the symptoms of the problem.
2 Look up the symptoms in this manual using the Table of
Contents or the Search tool. Review the list of possible
causes of the symptom.
3 Check each possible cause or perform a test that narrows
the list of possible causes until the symptom is resolved.
The [Status] key
Be sure to also use the [Status] and [Info] keys on the GC
keypad while using this troubleshooting information. These
keys will display additional useful information related to the
status of the GC and its components.
Error conditions
If a problem occurs, a status message appears. If the
message indicates broken hardware, more information may
be available. Press the applicable component key (for
example, [Front Det], [Oven], or [Front Inlet]).
10
Agilent 7890A Troubleshooting
1
Concepts and General Tasks
Configurable Items to Always Keep Current
Certain configurable items in the GC must always be kept
current. Failure to do so will lead to reduced sensitivity,
chromatographic errors, and possible safety concerns.
Inlet and detector configuration
Be sure to configure the GC and all related components to
reflect an inlet or detector change. Below are some examples
of components to keep current after making changes to the
inlet or detector:
Liners: The appropriateness of liner type varies depending
on the GC inlet mode, for example split mode versus
splitless mode, and the analysis.
FPD filters: The FPD filters require different gas flows to
function properly. Configure the flow according to the FPD
filter installed (phosphorus versus sulfur).
FID and NPD jets: Use the jet appropriate for the type of
column installed (capillary column versus packed column).
Column configuration
Reconfigure the GC every time a column is trimmed or
changed. Also verify that the data system reflects the correct
column type, length, id, and film thickness. The GC relies on
this information to calculate flows. Not updating the GC
after altering a column causes incorrect flows, changed or
incorrect split ratios, retention time changes, and peak
shifts.
Automatic Liquid Sampler configuration
Keep the Automatic Liquid Sampler (ALS) configuration
up- to- date to ensure proper operation. ALS items to keep
current include injector position, installed syringe size, and
solvent and waste bottle usage.
Gas configuration
WA R N I N G
Agilent 7890A Troubleshooting
Always configure the GC appropriately when working with
hydrogen. Hydrogen leaks quickly and poses a safety concern if
too much of it is released into the air or into the GC oven.
11
1
Concepts and General Tasks
Reconfigure the GC every time the gas type is changed. If
the GC is configured to a gas other than what is actually
being plumbed, incorrect flow rates will result.
To confirm the gas configuration:
1 Press [Config].
2 Scroll to the appropriate detector or column item on the
display and press [Enter] to see the type of gas configured.
12
Agilent 7890A Troubleshooting
Concepts and General Tasks
1
To View the Run Log, Maintenance Log, and Event Log
The GC maintains internal event logs, each of which holds
up to 250 entries. Use these logs to troubleshoot problems,
especially when a message no longer appears on the display.
To access the logs, press [Logs] to toggle to the desired log.
The display will indicate the number of entries the log
contains. Scroll through the list.
Run Log
For each run, the run log records deviations from the
planned method. This log is overwritten at the start of each
run. The run log information can be used for Good
Laboratory Practice (GLP) standards and can be uploaded to
an Agilent data system. When the Run Log contains entries,
the Run Log LED lights.
Maintenance Log
The maintenance log contains an entry for each time an
Early Maintenance Feedback limit is reached, reset, or
changed. The log records details such as the counter item,
the counter value, the new counter value, and whether or
not the counter was reset (indicating a part replacement).
When the maintenance log is full, the GC overwrites entries,
beginning with the oldest.
Event Log
The event log records events such as shutdowns, warnings,
faults, and GC state changes (start run, stop run, and so
forth) that occur during GC operation. When the event log is
full, the GC overwrites entries, beginning with the oldest.
Agilent 7890A Troubleshooting
13
1
Concepts and General Tasks
Information to Obtain Before Calling Agilent for Service
Gather the following information before contacting Agilent
for service:
• Symptoms
• Problem description
• Hardware installed and parameters/configuration when
the error occurred (sample, supply gas type, gas flow
rates, detectors/inlets installed, and so forth)
• Any messages that appear on the GC display
• Results of any troubleshooting tests you have run
• Instrument details. Obtain the following information:
• GC serial number, which can be found on a sticker
located beneath the keypad on the bottom right corner
of the GC.
• GC firmware revision (press [Status], then [Clear])
• GC power configuration (located on a label on the back
panel of the GC to the left of the GC power cable)
• Oven configuration (fast- or slow- heating)
• Press the [Status] key to display previous Error, Not Ready,
and Shutdown messages.
To obtain service/support contact numbers, see the Agilent
Web site at www.agilent.com/chem.
14
Agilent 7890A Troubleshooting
Agilent 7890A Gas Chromatograph
Troubleshooting
2
ALS and Detector Symptoms
Plunger Errors 16
Vial Mishandled by ALS (7693A) 17
Alignment Light on 7693A Injector Tower is On 19
Vial Mishandled by ALS (7683) 20
Alignment Light on 7683B Injector Tower is On 22
Syringe Needle Bends During Injection into Inlet 23
FID Fails Leakage Current Test 24
NPD Fails Leakage Current Test 25
FID Fails Baseline Test 26
To Resolve Low Sensitivity with an FID 27
FID Does Not Ignite 28
FID Ignitor Does Not Glow During Ignition Sequence 29
Corrosion in FID Collector and Ignitor Glow Plug 31
FPD Does Not Ignite 32
NPD Adjust Offset Process Fails 34
NPD Bead Will Not Ignite 35
Shutdown (Defective) Device 36
Agilent Technologies
15
2
ALS and Detector Symptoms
Plunger Errors
If the ALS reports a front or back plunger error, check the
following possible causes:
• The syringe plunger is sticking or is not securely
connected to the plunger carrier.
• The plunger solenoid is binding.
• The plunger carrier encoder is inoperable.
• The autoinjector plunger carrier mechanism will not
move.
• The plunger does not move freely due to sample residue
or wear. Install a new syringe, making sure to prime the
syringe with solvent before installing.
Procedure
1 Remove the syringe and check it for plunger stickiness or
binding. Replace the syringe if necessary (7693A, 7683).
2 Check the viscosity of the sample against the viscosity
parameter. Reset the viscosity parameter if necessary.
3 Restart the sequence.
4 If the error occurs again, obtain Agilent service.
16
Agilent 7890A Troubleshooting
ALS and Detector Symptoms
2
Vial Mishandled by ALS (7693A)
Refer to your sampler operating documentation for
additional information.
When you find a mishandled sample vial, do the following:
• Check for folds or wrinkles in the crimp cap, especially
near the neck of the sample vial.
• Use Agilent- recommended sample vials.
The figure below shows the critical dimensions for sample
vials and microvial inserts to be used with the 7693A ALS
system. These dimensions do not make up a complete set
of specifications.
Body Diameter (BD) = 11.7 ± 0.2
Cap Diameter (CD) = BD × 1.03 maximum
All dimensions in millimeters
CD
6.25 ± 0.25
3.7 min.
8.2 ± 0.2
33.5 ± 1.5
Vial plus cap height
32 ± 0.5
25 minimum
body height
11.7 ± 0.2
BD
Maximum height of a capped vial
Crimp cap sample vial
• Verify the transfer turret is installed if using a G4514A
tray.
• Check sample labels (if applicable).
• Check that they are the correct size.
• Verify that the labels do not interfere with the gripper.
Vials are available with a write- on spot for easy marking.
If you choose to make and apply your own labels, Agilent
Technologies recommends the positioning and maximum
label thickness shown in the figure below.
Agilent 7890A Troubleshooting
17
2
ALS and Detector Symptoms
All dimensions in millimeters
13.2 maximum
Text areas are optional
Text
3.6 min.
26.6 max.
Overlap mismatch
1.0 max.
Bar code
Text
13.4 minimum
No label or tape
16.4 ± 0.5
Label skew
12.56
Maximum width
measured at overlap
• Check that the tray vial racks are clean and snapped into
the tray base.
• Calibrate the system.
18
Agilent 7890A Troubleshooting
ALS and Detector Symptoms
2
Alignment Light on 7693A Injector Tower is On
If the Align Mode light is on, first verify that the turret is
properly installed. Then, perform the alignment procedure as
described in the 7693A Automatic Liquid Sampler
Installation, Operation and Maintenance manual.
Agilent 7890A Troubleshooting
19
2
ALS and Detector Symptoms
Vial Mishandled by ALS (7683)
Refer to your sampler operating documentation for
additional information.
When you find a mishandled sample vial, do the following:
• Check for folds or wrinkles in the crimp cap, especially
near the neck of the sample vial.
• Use Agilent- recommended sample vials.
• The distance from the vial bottom to the top of the
neck should be approximately 28.4 mm.
• The bottle neck diameter should be 8.2 ± 0.2 mm. The
sampler injector and the tray use clear or amber glass
sample vials with crimp caps, or Target® DP™
screw- cap vials. Use amber glass vials for
light- sensitive samples. Refer to your Agilent catalog
for consumables and supplies for acceptable vial types.
Incompatible sample vials cause tray and turret errors.
The figure below shows the critical dimensions for sample
vials and microvial inserts to be used with the sampler.
These dimensions do not make up a complete set of
specifications.
5 minimum
6.25 ± 0.25
3.7
8.2 ± 0.2
34.5
maximum
32 ± 0.5
11.7 ± 0.2
Microvial insert
Crimp cap sample vial
Maximum height of a
capped vial
All dimensions in millimeters
20
Agilent 7890A Troubleshooting
2
ALS and Detector Symptoms
• Verify the transfer turret is installed if using a tray and
G2913A injector.
• Check sample labels (if applicable).
• Check that they are the correct size.
• Verify that the labels do not interfere with the gripper.
Vials are available with a write- on spot for easy marking.
If you choose to make and apply your own labels, Agilent
Technologies recommends the positioning and maximum
label thickness shown in the figure below.
All dimensions in millimeters
0.2
No label or tape
0.44
Bar code
3.6 min.
5.6 ± 0.6
20.5 ± 1.0
Text
No label or tape
• Check that the tray vial racks are clean and snapped into
the tray base.
• If the tray cannot deliver or retrieve vials from a bar code
reader:
1 Press [Config].
2 Scroll to and select Sample tray.
3 Scroll to Grip offset and press [Mode/Type].
4 Scroll to the desired adjustment (Up, Default, or Down)
and press [Enter].
• If the sample vial touches the side of the turret hole as
the vial is raised or lowered, adjust the turret rotation.
For 7683B, adjust the gripper height as follows:
1 Press [Config].
2 Scroll to and select Sample tray.
3 Scroll to Front injector offset and press [Mode/Type].
4 Scroll to the desired adjustment (Clock, Counterclock, or
Default) and press [Enter].
Agilent 7890A Troubleshooting
21
2
ALS and Detector Symptoms
Alignment Light on 7683B Injector Tower is On
Refer to the 7683B Automatic Liquid Sampler Installation,
Operation and Maintenance manual for additional
information.
When the Align Mode light is on, the injector will not
operate until the following procedure is performed:
1 When the injector is not operating, open the injector
tower door.
2 Slide the syringe carriage up until it stops.
3 Remove the syringe.
4 Carefully remove the needle support assembly from the
injector.
5 Use a pen to press the recessed alignment button located
above the indicator lights, then close the door.
6 The injector will then go through the following steps:
a The turret rotates to verify that the needle support
assembly was removed, then rotates to determine what
type of turret is installed.
b The syringe carriage moves all the way down, then
moves back up again and clears the turret.
c The syringe carriage steps down until it touches the
turret. This sets its position relative to the turret.
d The plunger moves to calibrate six stops. Observe each
of the six steps to verify the plunger loop is
functioning properly. If it is missing stops, send the
injector to Agilent for repair.
7 When the alignment is complete, the Ready light turns on
and the sampler returns to the ready state. Install the
needle support assembly and syringe.
22
Agilent 7890A Troubleshooting
2
ALS and Detector Symptoms
Syringe Needle Bends During Injection into Inlet
WA R N I N G
When troubleshooting the injector, keep your hands away from
the syringe needle. The needle is sharp and may contain
hazardous chemicals.
Refer to your ALS documentation for additional information:
7683B Automatic Liquid Sampler Installation, Operation
and Maintenance
7693A Automatic Liquid Sampler Installation, Operation
and Maintenance
• Check that the GC septum nut is not too tight.
• Check that the syringe is installed correctly into the
syringe carriage.
• Check that the needle support and guide are clean.
Remove any residue or septum deposits. Install a new
needle support assembly (7683) or needle support foot
(7693A) if necessary.
• If using the cool on- column inlet, check that the correct
insert for the syringe is installed. See To Check the
Needle- to- Column Size on the COC Inlet for more
information.
• Check that you are using the proper syringe. The
combined length of the syringe barrel and needle should
be approximately 126.5 mm.
• Check that the sample vial dimensions meet specification.
See “Vial Mishandled by ALS (7693A)” or “Vial
Mishandled by ALS (7683)”.
• Check that the crimp cap is properly installed. Refer to
your sampler documentation.
Agilent 7890A Troubleshooting
23
2
ALS and Detector Symptoms
FID Fails Leakage Current Test
Possible causes
A failed leakage current test usually indicates misassembly,
contamination, or a damaged part.
Procedure
1 If you have just performed maintenance on the FID, first
verify that the detector was reassembled properly before
troubleshooting detector problems.
2 Replace the Teflon (FID) for contamination.
3 Make sure that the interconnect spring is not damaged,
bent, or dirty. The interconnect spring should be touching
the bottom of the collector. If the inteconnect spring is
damaged, bent, or dirty, call Agilent for service.
FID interconnect
spring
24
Agilent 7890A Troubleshooting
2
ALS and Detector Symptoms
NPD Fails Leakage Current Test
A failed leakage current test usually indicates misassembly,
contamination, or a damaged part.
If you have just performed maintenance on the NPD, first
verify that the detector was reassembled properly before
troubleshooting detector problems.
1 Replace the ceramic insulators. Restest.
2 Set the bead voltage to 0.0 V. Turn off the adjust offset.
View the output (leakage current).
3 Remove the bead and store in a safe place.
4 Remove the three screws that secure the lid in place, then
remove the lid.
5 Examine the interconnect spring. Make sure that the
interconnect spring is not damaged, bent, or dirty. The
interconnect spring should be touching the bottom of the
collector. If the inteconnect spring is damaged, bent, or
dirty, call Agilent for service.
Correct
6 If the interconnect spring is not damaged or dirty, and
the detector output signal is still high, contact Agilent for
service.
Agilent 7890A Troubleshooting
25
2
ALS and Detector Symptoms
FID Fails Baseline Test
If you have just performed maintenance on the FID, first
verify that the detector was reassembled properly before
troubleshooting detector problems.
If the FID fails the baseline test:
• Ensure the purity and quality of the gas.
• Replace dirty/expended chemical traps.
• Bakeout the detector.
26
Agilent 7890A Troubleshooting
ALS and Detector Symptoms
2
To Resolve Low Sensitivity with an FID
See “To Resolve Low Sensitivity with an FID”.
Agilent 7890A Troubleshooting
27
2
ALS and Detector Symptoms
FID Does Not Ignite
• Verify that the Lit Offset is < 2.0 pA.
• Ensure that the FID temperature is high enough for
ignition (>150 °C). Agilent recommends >300 °C.
• Check that the FID ignitor glows during ignition sequence.
(See To Verify FID Ignitor Function During Ignition
Sequence.)
• Check that the air and hydrogen pressures meet Agilent’s
recommendations (hydrogen > 35 psi [210 kPa] and air >
55 psi [380 kPa]). See the Agilent GC, MS, and ALS Site
Preparation Checklist.
• Try increasing the supply pressures to the FID flow
module. This makes the flame easier to light without
changing the setpoints.
• Increase hydrogen and air flow rates until ignition occurs,
then reduce them toward the method values. Experiment
for the best values.
• Check for a plugged or partially plugged jet. (See To
Check for a Plugged FID Jet.)
• Check the FID flow rates. Actual flow rates should be
within +/- 10% of the setpoint. (See FID starting
conditions.) The hydrogen:air ratio greatly impacts
ignition. Nonoptimal flow settings can prevent flame
ignition. (See To Measure a Detector Flow.)
• There could be a large leak in the system if the flame still
will not light. Large leaks result in measured flow rates
being different from actual flow rates, causing nonideal
ignition conditions. Thoroughly leak check the whole
system, especially the column fitting at the FID. (See
Checking for Leaks).
• Check the column flow rate. (See To Measure a Column
Flow.) Hydrogen flow should be greater than the sum of
the column flow and makeup flow.
• If the analysis permits, substitute nitrogen for helium as
makeup.
28
Agilent 7890A Troubleshooting
2
ALS and Detector Symptoms
FID Ignitor Does Not Glow During Ignition Sequence
WA R N I N G
Keep body parts at a safe distance from the FID chimney while
performing this task. If using hydrogen, the FID flame will not be
visible.
1 Remove the detector top cover.
2 Turn the FID flame On.
3 Observe the ignitor plug though the FID chimney. The
small hole should glow during ignition sequence.
If the test fails, check for the following possible causes:
• The ignitor may be bad; replace the ignitor. (See To
Perform Maintenance on the FID Collector Assembly.)
• Detector temperature is set to < 150 °C. Agilent
recommends operating the FID at > 300 °C.
• The ignitor is not making a good connection to the
ground:
• The ignitor must be tightly screwed into the FID castle
assembly.
• The three T- 20 Torx screws that hold the collector
assembly in place must be tight.
Agilent 7890A Troubleshooting
29
2
ALS and Detector Symptoms
• The brass knurled nut that holds the FID castle
assembly in place must be tight.
Perform FID maintenance if these parts are corroded or
oxidized.
T-20 Torx screws (3)
Ignitor
Knurled nut
30
Agilent 7890A Troubleshooting
ALS and Detector Symptoms
2
Corrosion in FID Collector and Ignitor Glow Plug
Agilent recommends inspecting the collector and ignitor glow
plug for corrosion while performing maintenance on the FID.
The FID combustion process results in condensation. This
condensation, combined with chlorinated solvents or
samples, causes corrosion and sensitivity loss.
To avoid corrosion, keep the detector temperature above
300 °C.
Agilent 7890A Troubleshooting
31
2
ALS and Detector Symptoms
FPD Does Not Ignite
• Check that the FPD temperature is high enough for
ignition (> 150 °C).
• Check FPD flow rates and that they match the type of
filter installed in the FPD. The hydrogen:air ratio greatly
impacts ignition. Nonoptimal flow settings can prevent
flame ignition.
Table 1
FPD recommended flows
Sulfur mode flows,
mL/min
Phosphorus mode
flows, mL/min
Carrier (hydrogen, helium, nitrogen, argon)
Packed columns
10 to 60
10 to 60
Capillary columns
1 to 5
1 to 5
Hydrogen
50
75
Air
60
100
Carrier + makeup
60
60
Detector gases
• Measure the actual detector flows. (See To Measure a
Detector Flow.)
• The column may be installed too high into the detector.
• Check that the FPD ignitor operates. (See To Verify That
the FPD Flame Is Lit.)
• During the ignition sequence, display the air flow rate.
The air flow rate should go to 200 mL/min while trying
to ignite to flame. If not, there is insufficient supply
pressure.
• Check the column and makeup flow rates.
• Ensure that condensation in the vent tube is not dripping
back into the detector. The flexible plastic vent tube must
run from the detector into a container, without sagging,
in order to properly drain water condensate. Keep the
open tube end out of the water in the container.
• Check the Lit offset value. The typical Lit offset value is 2.0.
If it is zero, autoignition is turned off. If it is too large,
the software will not recognize that the flame is lit and
will shut the detector down.
32
Agilent 7890A Troubleshooting
2
ALS and Detector Symptoms
• If the flame still will not light, there could be a large leak
in the system. This results in measured flow rates being
different from actual flow rates, causing non- ideal ignition
conditions. Thoroughly leak check the whole system. (See
Checking for Leaks.)
• Try increasing the supply pressures to the FPD flow
module. This makes the flame easier to light without
changing the setpoints.
• Under some operating conditions, the flame may be more
easily lit with the rubber drip tube removed. After
lighting the flame, reinstall the drip tube.
• The sulfur mode can be particularly hard to light. Try
changing to the phosphorus mode flows, lighting the
flame, and gradually alter the flows to the sulfur values.
• Check cable connections to coupling, coupling connection
to glow plug, tight glow plug.
Agilent 7890A Troubleshooting
33
2
ALS and Detector Symptoms
NPD Adjust Offset Process Fails
• Inspect the jet to see if it is clogged. (See To Check for a
Plugged NPD Jet.)
• Measure the actual detector flows. (See To Measure a
Detector Flow.) If the hydrogen or makeup flows are zero
or much lower than the displayed flow, suspect a plugged
jet.
• Check the condition of the bead. Replace if necessary.
• Verify that the flow settings are correct. See Flows,
temperatures, and bead information.
• If the process still fails, there could be a large leak in the
system. This causes measured flow rates to be different
from actual flow rates. Thoroughly leak check the whole
system, especially the detector column fitting. (See
Checking for Leaks.)
• Set the equilibration time to 0.0.
34
Agilent 7890A Troubleshooting
ALS and Detector Symptoms
2
NPD Bead Will Not Ignite
• Set the equilibration time to 0.0.
• Verify that the flow settings are correct and appropriate.
See Flows, temperatures, and bead information.
• If the process still fails, there could be a large leak in the
system. This causes measured flow rates to be different
from actual flow rates. Thoroughly leak check the whole
system, especially the detector column/adapter fitting.
(See Checking for Leaks.)
• Check for fault messages. Press [Service Mode], then go to
Diagnostics > Front detector or Back detector > Detector signal.
You can also read the bead voltage.
• Check the condition of the bead. Replace if necessary.
• Inspect the jet to see if it is clogged. (See To Check for a
Plugged NPD Jet.)
• Measure the actual detector flows. (See To Measure a
Detector Flow.) If the hydrogen or makeup flows are zero
or much lower than the displayed flow, suspect a plugged
jet.
Agilent 7890A Troubleshooting
35
2
ALS and Detector Symptoms
Shutdown (Defective) Device
By default, the GC monitors the status of all configured
devices (inlets, detectors, valve box heaters, valves, oven
heater, EPC modules, and so forth) and becomes ready when
all of them reach setpoint. If the GC senses a problem in
one of these devices, the GC will either never become ready,
or may go into a shutdown state to protect itself or prevent
a safety hazard. However, there may be a time when you do
not wish to have the readiness state of a device prevent a
run from starting. An important example is when an inlet or
detector heater is defective. Normally, this fault prevents the
GC from becoming ready and starting a run. However, you
can set the GC to ignore this problem so that you can use
the other inlet or detector until the device is repaired.
Not all devices can be ignored. You can ignore the readiness
state of inlets, detectors, the oven, or an EPC module. The
readiness state of other devices and components can never
be ignored, for example, injection devices such as a
switching valve or automatic liquid sampler.
To ignore the status of a device:
1 Turn off the device’s heater and gas flows as applicable.
(Make sure that it cannot create a safety hazard.)
2 Press [Config], then select the element.
3 Scroll to Ignore Ready and press [On/Yes] to set it to True.
You can now use the GC until the device is repaired.
CAUTION
Do not ignore the readiness state of a device that is being used
unless you do not care if it reaches setpoint.
Be sure to return a broken device to Ignore Ready = False after it is
repaired. Otherwise, its state (temperature, flow, pressure, and so
forth) will continue to be ignored, even if using this device in the
analysis.
To consider a device’s readiness, set Ignore Ready to False.
36
Agilent 7890A Troubleshooting
Agilent 7890A Gas Chromatograph
Troubleshooting
3
Chromatographic Symptoms
Retention Times Not Repeatable 38
Peak Areas Not Repeatable 39
Contamination or Carryover 40
Larger Peaks Than Expected 43
Peaks Not Displayed/No Peaks 44
Baseline Rise During Oven Temperature Program 46
Poor Peak Resolution 47
Peak Tailing 48
Peak Boiling Point or Molecular Weight Discrimination Poor 50
Sample Decomposition in Inlet/Missing Peaks 51
Peak Fronting 52
Noisy Detector, Including Wander, Drift, and Baseline Spikes 53
Microcell Electron Capture Detector (uECD) Noise and Sensitivity 59
Low Peak Area or Height (Low Sensitivity) 63
FID Flame Goes Out During a Run and Attempts to Reignite 66
FID Baseline Output Above 20 pA 68
FID Baseline Output at Maximum (~8 Million) 69
FPD Flame Goes Out During a Run and Attempts to Reignite 70
FPD Quenching/Repeatability 71
FPD Output Too High or Too Low 72
FPD Low Peak Areas 73
FPD Large Peak Width at Half-Height 74
FPD Baseline Output High, > 20 pA 75
FPD Chromatographic Output Showing Clipped Peaks 76
NPD Solvent Quenching 77
NPD Response Low 78
NPD Baseline Output > 8 million 80
NPD Adjust Offset Process Not Functioning Properly 81
NPD Low Selectivity 82
Negative Peaks Seen with TCD 83
TCD Baseline Has Dampened Sinusoidal Noise Trailing Peaks (Ringing
Baseline) 84
TCD Peaks Have Negative Dip on Tail 85
Agilent Technologies
37
3
Chromatographic Symptoms
Retention Times Not Repeatable
• Replace the septum.
• Check for leaks in the inlet, liner (as applicable), and
column connection. (See “Checking for Leaks”.)
• To Perform an Inlet Leak Check
• To Check for Leaks in a Split/Splitless Inlet
• To Perform a PP Pressure Decay Leak Test
• To Check for Leaks in a Multimode Inlet
• To Perform a COC Pressure Decay Leak Test
• To Perform a PTV Pressure Decay Test
• To Perform a VI Pressure Decay Test
• Check for sufficient carrier gas supply pressure. The
pressure delivered to the GC must be at least 40 kPa
(10 psi) greater than the maximum inlet pressure
required at final oven temperature.
• Run replicates of known standards to verify the problem.
• Verify that you are using the correct liner type for the
sample being injected. (See Selecting the correct inlet
liner.)
• Consider if this is the first run. (Has the GC stabilized?)
• If using an FID or NPD and retention times increase
(drift), check the jet for contamination or replace the jet.
• To Replace an FID Jet
• To Check for a Plugged FID Jet
• To Maintain the NPD Collector, Ceramic Insulators, and
Jet
• To Check for a Plugged NPD Jet
38
Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
Peak Areas Not Repeatable
Check the ALS syringe operation. (See the Troubleshooting
section of the 7693A Automatic Liquid Sampler Installation,
Operation and Maintenance and 7683B Automatic Liquid
Sampler Installation, Operation and Maintenance manuals.)
• Replace the syringe.
• Check for leaks in the inlet, liner (as applicable), and
column connection. (See “Checking for Leaks”.)
• Check sample level in vials.
• Run replicates of known standards to verify the problem.
• Consider if this is the first run. (Has the GC stabilized?)
For a multimode or split/splitless inlet in split mode, also
check for:
• An abnormal split vent restriction. See:
• To Run the Inlet Trap Check
• To Perform a SS Split Vent Restriction Test.
• To troubleshoot small leaks in a multimode or
split/splitless inlet, see To Check for Leaks in a
Split/Splitless Inlet or To Check for Leaks in a Multimode
Inlet.
Agilent 7890A Troubleshooting
39
3
Chromatographic Symptoms
Contamination or Carryover
If your output has contamination or unexpected peaks, do
the following:
Isolate the source
1 Perform a solvent blank run using a new, pure source of
solvent. If the contamination disappears, the problem may
be either in the sample or solvent- related.
2 Perform a blank run (remove the syringe from the injector
and start a run). If the contamination disappears, the
problem is in the syringe.
3 Remove the column from the detector and cap the
detector fitting. Perform another blank run. If the
contamination disappears, the problem is in the inlet or
column. If the contamination remains, the problem is in
the detector.
Check possible causes—all inlet and detector combinations
Inlet, sampler, sample, gas supply
• Check the septum type and installation. The vial septum
may be dissolving in the sample. Be sure the vial septum
is resistant enough to the solvent you are using. Also
ensure the vial septum is flat. If the vial septum is not
flat, the needle tends to core the septum and drop pieces
into the sample, causing contamination and ghost peaks.
• Perform complete inlet maintenance: Replace all
consumable parts and bake out the inlet.
• Check for sample carryover from previous runs. Make
several no- injection blank runs and see if the ghost peaks
go away or get smaller.
• Check the septum purge flow. If it is too low, the septum
may have collected contamination or condensate may be
clogged in the purge line. For SS, MMI, PTV, and PP
inlets: Set the purge flow to at least 3 mL/min to keep
the septum clean. For COC inlets, set the septum purge
flow to at least 15 mL/min. Measure the flow. See “To
Measure a Column Flow””.
• Check all gas trap indicators and dates.
40
Agilent 7890A Troubleshooting
3
Chromatographic Symptoms
• Verify the gas purity. Perform replicate runs, several with
a short interval between them, then several with a large
interval. If the contamination peaks are larger for the
runs made with the longer interval, suspect contaminated
gas: the contamination has more time to deposit onto the
column and liner.
• Check for supply tubing and fitting contamination.
• If you suspect that there is contamination in the inlet,
perform the bakeout procedure (SS, MMI, PP, COC, PTV,
VI).
• Verify the operation of the inlets. Clean the inlet and
replace the contaminated inlet parts.
• To Clean the Split/Splitless Inlet
• To Clean the Purged Packed Inlet
• To Clean the Cool On- Column Inlet
• To Clean the Septumless Head on the PTV Inlet
• To Clean the Multimode Inlet
• To Clean the Septum Seat in the Septum Head
Assembly of the PTV Inlet
• To Clean the VI
• Check the solvent level in the ALS wash bottles.
• Replace the ALS syringe if necessary (7693A, 7683).
• Check the sample injection volume. Verify that the ALS is
injecting enough sample into the inlet. Use the Solvent
Vapor Volume Calculator to determine how much of the
sample should be injected.
• Ghost peaks are sometimes caused by contaminated
sample vials. Try new or clean vials to see if ghost peaks
disappear.
• Some samples change with heat or ultraviolet light. Check
the sample stability.
Column, method
• Perform column maintenance: Bake out contaminants,
remove the contaminated length of column near the inlet,
and reverse and bake out the column as needed.
• If you suspect that there is contamination in the column,
perform the bakeout procedure.
Agilent 7890A Troubleshooting
41
3
Chromatographic Symptoms
• Verify that the oven program temperature and time are
sufficient for the samples being injected. Ghost peaks that
are broader than adjacent sample peaks could be from a
previous run.
• Inspect the column for contamination. High molecular
weight samples that contain residues may cause the
syringe, the inlet liner, or the first few inches of column
to become contaminated.
• Install an Agilent column backflush system.
Detector, detector gas supply
• Check all gas trap indicators and dates.
• Verify the gas purity. Perform replicate runs, several with
a short interval between them, then several with a large
interval. If the contamination peaks are larger for the
runs made with the longer interval, suspect contaminated
gas: the contamination has more time to deposit onto the
column and liner.
• Check for supply tubing and fitting contamination.
• If you suspect that there is contamination in the detector,
perform the bakeout procedure (FID, TCD, uECD).
• Verify the operation of the detectors. Replace the
contaminated detector parts.
• To Maintain the NPD Collector, Ceramic Insulators, and
Jet
• Maintaining the FID
42
Agilent 7890A Troubleshooting
3
Chromatographic Symptoms
Larger Peaks Than Expected
• Check each configured column’s dimensions against the
actual column dimensions. (See “Configurable Items to
Always Keep Current”.) Refer to To configure a single
column or To configure multiple columns in the Advanced
User Guide for procedures on configuring columns.
• Check the autosampler injection volume. In the normal
injection mode, the sampler uses fast injection to deliver
a representative amount of the sample. Fast injection
minimizes needle fractionation. Chromatograms from
manual injection or slower auto injection devices show
higher levels of low molecular weight materials versus
higher molecular weight materials because the volatiles
boil out of the needle faster than the higher weight
materials.
• Check the vial caps. Loose vial caps can cause selective
loss of lighter materials from a sample. The cap should
not rotate easily if installed properly.
• Check configured syringe size. Some syringe sizes are
specified at half- capacity. If the maximum syringe volume
is marked at half- height on the barrel, not at the top of
the barrel, enter twice the labeled volume when
configuring the syringe size.
Agilent 7890A Troubleshooting
43
3
Chromatographic Symptoms
Peaks Not Displayed/No Peaks
• If using an autosampler:
• Ensure that there is sample in the vial.
• Verify that the ALS plunger carriage is secured to the
syringe plunger.
• Check that the syringe is installed correctly (7693A or
7683B) and draws sample.
• Verify that the turret/tray is loaded correctly and
injections are not from out- of- sequence vials.
• Watch to see that the sample is pulled into the syringe.
• Verify the detector in use is assigned to a signal.
• Check the column for proper installation.
• Ensure that the column is not plugged. (See “To Measure
a Column Flow”.) Perform column maintenance.
• Check for leaks. (See “Checking for Leaks”.)
• Check the flow settings, then measure the actual detector
flows. (See “To Measure a Detector Flow”.)
• Some samples change with heat or ultraviolet light. Check
sample stability.
• Check the sample level in the vial.
• If the sample is viscous, try the following:
• Increase the viscosity delay time.
• Dilute the sample in an appropriate low- viscosity
solvent.
• Turn the tower fan off.
• For 7683B ALS, use the tray quadrants to warm the
sample. For 7693A ALS, use the vial heater (accessory
G4514A Bar Code Reader/Mixer/Heater) to warm the
sample vial.
If the problem is with the detector, see Table 2.
Table 2
44
Detector troubleshooting
Detector
Solution
FID, FPD
• Verify that the electrometer is turned on.
• Verify that the flame is still lit.
Agilent 7890A Troubleshooting
Chromatographic Symptoms
Table 2
3
Detector troubleshooting
Detector
Solution
TCD
• Verify that the filament is turned on.
• Ensure that the reference gas is not set to zero. (The
filament will not turn on with zero reference gas flow.)
Agilent 7890A Troubleshooting
45
3
Chromatographic Symptoms
Baseline Rise During Oven Temperature Program
• Inspect the column for bleed.
• Check for leaks/oxygen in carrier gas supply. Oxygen can
damage bonded phase capillary columns.
• Check gas supply oxygen trap indicator or date.
• Make solvent blank runs to evaluate baseline without
sample.
• Make “no injection” blank runs (remove the syringe from
the injector and start a run) to evaluate baseline without
solvent.
• Check for contamination. (See Contamination or
Carryover.)
• Consider the effect of column film thickness on bleed. Try
using a column with a thinner film.
• Check for leaks at the column fittings. (See “Checking for
Leaks”.)
• Prepare and use a column compensation profile.
46
Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
Poor Peak Resolution
• Set column flow to optimum linear velocity.
• Install and use deactivated consumable parts in the inlet
(for example, a liner).
• Perform column maintenance: Bake out contaminants,
remove the contaminated length of column near the inlet,
and reverse and bake out the column as needed.
• Check column installation at both ends.
• Select a higher resolution column.
Agilent 7890A Troubleshooting
47
3
Chromatographic Symptoms
Peak Tailing
The figure below shows an example of tailing peaks. When
troubleshooting tailing peaks, consider:
• Which peaks are tailing?
• Are the tailing peaks active compounds, all compounds, or
are there trends (such as early eluters or late eluters)?
• Check the column for severe contamination.
• If using a capillary column, remove 1/ 2 to 1 meter
from the front of the column.
• For bonded and cross- linked phases, solvent rinse the
column.
• Check for inlet contamination. Tailing will sometimes
increase with compound retention. Clean the inlet and
replace contaminated inlet parts. (See the 7890A
Maintenance manual.)
• Consider the column stationary phase (active column).
This only affects active compounds. An active column
usually produces tailing that increases with retention
time.
• Cut off 1 meter from the front of the column.
• Replace the column.
• Verify that the column was cut and installed properly.
• Re- cut and reinstall the column into the inlet and
replace the ferrules. Make a clean, square cut using a
reliable tool.
• Confirm the installation is leak free. If there is a leak
at the column fitting, you will see more tailing for
early eluting peaks. (See “Checking for Leaks”.)
• Consider the type of adapter, liner, and inlet seal being
used. One or all of these may be contaminated or active.
48
Agilent 7890A Troubleshooting
3
Chromatographic Symptoms
• Use a new, deactivated liner. This only affects active
compounds.
• Clean or replace the inlet seal.
• Check adapters (if installed) and liner for solid particles.
If solid particles are visible, clean or replace.
• For capillary splitless injection, consider compatibility
between the solvent and column.
• Use a different solvent. This will help in instances
where there is more tailing for the early eluting peaks
or those closest to the solvent front.
• Use a 3 to 5 meter retention gap.
• Verify that the injection technique is adequate. This is
usually related to erratic plunger depression or having
sample in the syringe needle.
• Verify the inlet temperature.
• If the temperature is too high, tailing is generally
worse for early eluters. Decrease inlet temperature by
50 °C.
• If the temperature is too low, tailing usually increases
with retention. Increase inlet temperature by 50 °C.
• Check for dead volume in the system. Check for correct
column installation at both ends.
• If peak tailing decreases with retention time, reduce
dead volume in transfer line connections, fused silica
unions, and so forth.
• A column installed too high into a detector or inlet can
create dead volume areas.
• Inspect any transfer lines for cold spots. Cold spots cause
tailing that usually increases with retention time.
NPD Peak Tailing
For NPD, do the following:
• Verify that you are using the correct bead for the sample
being run. If you are analyzing phosphorus, install a black
bead. White beads can cause peak tailing when
phosphorus is being analyzed.
• Verify that the correct jet is installed. Use an extended
jet.
• Replace the ceramic insulators.
Agilent 7890A Troubleshooting
49
3
Chromatographic Symptoms
Peak Boiling Point or Molecular Weight Discrimination Poor
If you have trouble with peak boiling point or molecular
weight discrimination (inlet discrimination), do the following:
• Check the inlet for contamination. Clean and change the
liner if necessary. Replace all inlet consumable parts. See
the Maintenance manual.
• Adjust the inlet temperature.
• Run standards against a known method to determine
expected performance.
For any inlet operating in split mode with any detector
• Check liner type. Use a liner optimized for split
analysis—one that contains glass wool or other surface
area packing to allow complete sample vaporization.
• Increase the inlet temperature and verify that the
insulation cup is installed and contains insulation.
• Check column cut and installation into the inlet. See the
topic for the SS, MMI, PTV, and VI.
For any inlet operating in splitless mode with any detector
• Check the inlet for leaks. (See “Checking for Leaks”.)
• Check liner type. Use a liner optimized for splitless
analysis (deactivated, large volume).
• Verify that the oven starting temperature is less than the
solvent boiling point.
• Check column cut and installation into the inlet. See the
topic for the SS, MMI, PTV, and VI.
• Check that the solvent vapor volume does not exceed the
liner capacity.
• Check for appropriate purge delay time. (Liner
volume/column flow)
50
Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
Sample Decomposition in Inlet/Missing Peaks
• Lower the inlet temperature.
• Check for air or water in the carrier gas; verify gas purity
and functionality of traps.
• Verify that the liner is appropriate for the sample being
run.
• Perform complete inlet maintenance: Replace all
consumable parts and bake out the inlet.
• Install a deactivated liner (if liner is used).
• Check for leaks at the septum, liner, and column fittings.
(See “Checking for Leaks”.)
• Install an Agilent Direct Connect liner.
• Use a pulsed pressure method for quicker sample transfer
to column.
• Bake out the inlet. See the following:
• To Bakeout Contaminants from the Split/Splitless Inlet
• To Bakeout Contaminants from the Multimode Inlet
• To Bakeout Contaminants from the Purged Packed Inlet
• To Bakeout Contaminants from the COC Inlet
• To Bakeout Contaminants from the PTV Inlet
• To Bakeout Contaminants from the VI Inlet
• Clean the inlet. See the following:
• To Clean the Split/Splitless Inlet
• To Clean the Multimode Inlet
• To Clean the Purged Packed Inlet
• To Clean the COC Inlet
• To Clean the Septumless Head on the PTV Inlet
• To Clean the Septum Seat in the Septum Head
Assembly of the PTV Inlet
• To Clean the VI
Agilent 7890A Troubleshooting
51
3
Chromatographic Symptoms
Peak Fronting
The figure below shows examples of the three types of
peaks: symmetric, fronting, and overloaded.
Symmetrical
Fronting
Overloaded
If peak fronting or overloading occurs, try the following:
• Verify that the injection volume is appropriate. Column
overload is the most common cause for fronting peaks.
• Decrease injection volume, dilute the sample, and/or
increase the split ratio.
• Change the column type or film thickness.
• Ensure that the column is installed properly. If not,
reinstall the column in the inlet.
• Verify that the appropriate injection technique is being
used. This is usually related to erratic plunger depression
or having sample in the syringe needle.
• If using capillary splitless injection, consider the
compound solubility in the injection solvent.
• Change the solvent.
• Use a retention gap.
• Check purity of sample solvent. For solvents with large
differences in polarity or boiling points, a mixed sample
solvent can cause peak fronting. Change the sample
solvent.
52
Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
Noisy Detector, Including Wander, Drift, and Baseline Spikes
Noise should be measured under “normal” operating
conditions, with a column connected and carrier gas on. FID
electrometer noise or drift (flame off), for instance, will not
provide much indication of how the detector will perform in
practice because major sources of noise are not included in
this measurement. Noise typically has a high frequency
component (electronic in origin) and lower frequency
components that are referred to as wander and drift.
Wander is random in direction but at a lower frequency than
the short- term electronic noise. Long- term noise (drift) is a
monotonic change in signal over a period that is long
compared to the wander and electronic noise (see below).
Terms like “short” and “long” are relative to the width of the
chromatographic peaks. In general, one should measure
noise over a period of time that is about 10 times the peak
width at half height (or 10 times the area/height ratio for a
Gaussian peak). Measuring for longer times can
over- estimate noise; shorter times may underestimate noise.
Total noise
Long-term noise (drift)
Wander
Short-term noise
Noisy baseline
A noisy baseline or high detector output can indicate leaks,
contamination, or electrical problems. Some noise is
inevitable with any detector, although high attenuations can
mask it. Since noise limits useful detector sensitivity, it
should be minimized.
• For all detectors, check for leaks at the column fittings.
(See “Checking for Leaks”.)
• For the FID, see To Isolate the Cause of FID Noise.
• For the TCD, verify data collection at < 5 Hz.
Agilent 7890A Troubleshooting
53
3
Chromatographic Symptoms
If noise appears suddenly on a previously clean baseline, do
the following:
• Consider recent changes made to the system.
• Bakeout the inlet. See the following:
• To Bakeout Contaminants from the Split/Splitless Inlet
• To Bakeout Contaminants from the MMI Inlet
• To Bakeout Contaminants from the Purged Packed Inlet
• To Bakeout Contaminants from the COC Inlet
• To Bakeout Contaminants from the PTV Inlet
• To Bakeout Contaminants from the VI Inlet
Bakeout can reduce septum bleed and other
contaminants. New septa may contribute noise from bleed
of low molecular weight material. If noise decreases when
inlet temperature is lowered, this is a likely cause. Use
only high quality septa and store them where they cannot
become contaminated.
• Verify the purity of carrier and detector gases. If a tank
was replaced recently and the old one is still available
and still has some gas in it, try the older tank to see if
noise decreases.
If the new gas is so badly contaminated that it saturates
traps, changing to the old one may show little
improvement until the traps are replaced or regenerated.
This problem is most common with nitrogen carrier gas.
Deal with a reliable gas supplier.
• For the TCD, check for ambient air pressure fluctuations
at the GC. Air currents from a fan or air conditioner
blowing across the GC may interfere with gas exiting the
detector. This is a possible, though not very likely cause
of noise since detectors are well protected. Switching off
the air current source or shielding the detector exit
identifies this problem. Install the TCD outlet restrictor
(G1532- 60070).
• Loose connections in the detector or its signal path
generate noise.
• Verify proper reassembly after recent maintenance.
• Inspect the detector for contamination.
If noise increases gradually to an unacceptable level, check
the following possible causes:
• Bakeout the detector (FID, TCD, uECD).
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Chromatographic Symptoms
• Inspect the detector for contamination. Replace parts as
needed. (See the 7890A Maintenance manual.)
• Inspect the column and inlet for contamination.
• Inspect the FID or NPD jet for contamination.
• To Check for a Plugged FID Jet
• To Replace an FID Jet
• To Check for a Plugged NPD Jet
• To Maintain the NPD Collector, Ceramic Insulators, and
Jet
• Verify that the FPD photomultiplier tube (PMT) is
properly installed. If it is not, light leaks and ultimately
noise will result.
FIDs are susceptible to gradual buildup of deposits in the
detector. In extreme cases, spiking occurs along with
increased noise level.
Carbon (black) deposits may form from solvents that burn
poorly (primarily chlorinated materials and aromatics). Avoid
such solvents if possible. If you must use them, be prepared
to clean the detector regularly.
Silicon dioxide (white) is formed when bleed from a silicone
column is burned in the flame. To minimize this, use low
column loadings, select phases with high temperature limits,
condition columns thoroughly before use, and use the lowest
possible oven temperature for the analysis.
To remove either type of deposit, disassemble the detector
and scrub with a small brush. A solvent (almost anything
will do) helps flush away the particles. Agilent recommends
replacing dirty collector and insulator parts.
Other factors that can contribute to noise:
• Column installed too high into detector.
• Oven temperature exceeds column maximum
recommended temperatures.
Baseline wander and drift
Baseline wander or drift can occur when a flow or
temperature setting is changed. If the system has not
stabilized at the new conditions before it starts a run, some
baseline changes are to be expected. The following cases
assume that sufficient stabilization time has elapsed since
the last change in operating conditions.
Agilent 7890A Troubleshooting
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Chromatographic Symptoms
If experiencing baseline wander, check for leaks, especially
at the septum and at the column. (See “Checking for Leaks”.)
If the leak is at the detector end of the column, retention
times are stable from run to run but sensitivity is reduced.
If it is at the inlet end, sensitivity is reduced and retention
times are increased.
Also consider whether the oven temperature program is
sufficient.
Baseline drift is most often seen during temperature
programming. To correct baseline drift, do the following:
• Verify that column compensation is used and the profile
is current. (To compensate for bleed.)
• Verify that the column is conditioned.
• Check column bleed while at operating temperature.
• Check the signal mode assigned to the column in the data
system.
• Check the column compensation profile. It may be too
little (upscale drift) or too much (downscale drift).
This cause of drift is minimized by thorough column
conditioning. Operating at a lower temperature reduces
the drift but prolongs the analysis. Use of a
chromatographically equivalent column with a higher
temperature limit is also possible.
Baseline spiking
There are two types of spiking on the baseline output: cyclic
and random. Spiking will not normally be noticed on the
display; it will be noticed only on a plot or online trace.
Figure 1
Cyclic spiking
Cyclic spiking can be caused by the following:
• An electric motor
• Building heating/cooling system
• Other electronic interferences in the lab
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Agilent 7890A Troubleshooting
Chromatographic Symptoms
Figure 2
3
Random spiking
Spikes are isolated baseline disturbances, usually appearing
as sudden (and large) upscale movements. If accompanied by
noise, resolve the noise problem first since spiking may
disappear at the same time.
• Check for a contaminated detector. In an extremely dirty
FID, particles of carbon or silicon dioxide may break
away and fall into the detection zone.
• For a packed column, check that the packed column exit
is properly sealed with glass wool. This will cause packing
particles to be blown into the detector. A defective or
missing glass wool plug at the exit of a packed column
will do this. This may happen with any detector but the
flame detector is particularly susceptible because of the
narrow bore of the jet.
• Check packed column installation. The bottom of the jet
or the end of a transfer tube extends into the end of the
column. If it touches a glass wool plug, spikes are
produced.
• Check for the correct jet. See the following:
• Selecting an FID jet
• To replace an FID jet
• Selecting an NPD jet
• To Maintain the NPD Collector, Ceramic Insulators, and
Jet
Agilent 7890A Troubleshooting
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Chromatographic Symptoms
• Check that the detector temperature is not too low. See
the following:
• Recommended starting conditions for new FID methods
• Selecting reference and makeup flows for the TCD
• Recommended starting conditions for new uECD
methods
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Chromatographic Symptoms
Microcell Electron Capture Detector (uECD) Noise and Sensitivity
CAUTION
Detector disassembly and/or cleaning procedures other than
thermal should be performed only by personnel trained and licensed
appropriately to handle radioactive materials. Trace amounts of
radioactive 63 Ni may be removed during these other procedures,
causing possible hazardous exposure to radiation.
WA R N I N G
To prevent possible hazardous contamination of the area with
radioactive material, the detector exhaust vent must always be
connected to a fume hood, or otherwise vented in compliance with
local regulations.
Performance problems associated with the ECD include (but
are not limited to) loss of sensitivity (real, or perceived),
high signal background, noisy baseline, and chromatographic
peaks or humps that are not characteristic of the samples
being injected.
If the problems are not accompanied by an increase in the
signal output, as read from the front keypad of the GC, then
suspect the detector only after the other parts of the
chromatographic system have been checked.
Before starting extensive troubleshooting, consider first the
nature of the problem:
1 If recent changes were made in the system, such as
changing carrier or detector gases, performing inlet or
column maintenance, or changing the column, investigate
the possibilities that contamination or leaks were
introduced.
2 If the problem has been chronic and is now acute enough
to interfere with analysis, suspect contamination, column
degradation, or ultimately a bad ECD cell.
See also:
“Display signal evaluation”
“Sensitivity”
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Chromatographic Symptoms
Display signal evaluation
The first consideration is the signal value when the GC is in
the idle state. The “idle” signal level is a function of the type
and quality of the carrier and detector gases, as well as the
flows and application. It may be different for different
situations but as a general rule, the following values apply
(Table 3). Figure 3 shows typical uECD life cycle stages.
Table 3
NOTE
uECD signal evaluation
ECD signal
Comments
<200
uECD is “healthy”.
200 to 400
Slightly elevated, no cause for concern
at this point. Signal still in “good”
range.
400 to 1000
System showing signs of
contamination from gases, column, or
samples. If the signal increases in
response to increased oven
temperature, suspect the column.
1000 to 2000
Suspect more severe contamination,
follow the troubleshooting guidelines.
>2000
If the following procedures do not
work, suspect the uECD cell.
It may take 24 hours for the uECD baseline to completely stabilize,
especially if you are starting with a cold system and want to assure
high-sensitivity operation. For the most accurate results, run the detector
at normal operating conditions for as long as possible (at least 2 hours and
up to 24 hours) before running the frequency test.
If you will be injecting into an unused inlet, you must use low-bleed septa.
Make sure to condition new septa before use in an inlet for several hours
with 1 to 5 mL/min carrier flow.
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Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
Typical ECD Life Cycle Stages:
1
2
3
4
5
Stage 1:
New cell
Background = 100 Hz. Cell meets Agilent signal-to-noise (S/N) standard.
Stage 2:
6 months – 1 year
Background = 180 Hz. Increased response.
Stage 3:
1–2 years
Background = 350 Hz. More response, increasing noise, lower S/N.
Stage 4:
2–4 years
Background > 500 Hz. Noisy baseline, negative peaks. Thermal cleaning required.
Stage 5:
4–10 years
Background > 1000 Hz. Huge response. Very noisy, cell contaminated. Requires cell exchange.
Figure 3
Typical ECD life cycle
Sensitivity
If the ECD is in the “good” signal range and sensitivity is
the issue, the problems quite likely may be in the inlet or
column. Consider the following issues:
1 If using an inlet with split and splitless modes, verify that
the mode has not changed and that the split valve is
functioning. This can be done by verifying that there is a
corresponding change in the response by making split and
then splitless injection, all other method parameters
remaining the same. If using split mode, verify the split
flow using a flow meter.
2 Check all flow rates. See “Measuring FID, TCD, uECD, and
FPD flows”.
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Chromatographic Symptoms
3 Confirm that complete inlet maintenance has been
performed. This includes trimming and re- installing the
column.
4 Verify that the injecting device is working properly. If the
method uses a sampling valve, make a direct syringe
injection of concentration similar to that introduced by
the valve. Rule out a problem with the valve.
5 Inspect the mixing liner in the makeup gas adapter. A
small piece of graphite or sample contamination will
reduce sensitivity. See To Replace the uECD Fused Silica
Indented Mixing Liner and Install the Makeup Gas
Adapter.
Contamination (high baseline)
If the ECD has a baseline higher than expected for its age,
check the following:
• Rule out all other possible causes. See “Sensitivity” above.
Also check carrier and detector gas supplies, supply gas
traps, and the column.
• Inspect the mixing liner in the makeup gas adapter. A
small piece of graphite can contaminate results. See To
Replace the uECD Fused Silica Indented Mixing Liner and
Install the Makeup Gas Adapter.
• If the detector baseline is > 500 Hz, regardless of detector
age, bakeout the detector. Let it run for 1–2 days.
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Chromatographic Symptoms
Low Peak Area or Height (Low Sensitivity)
• If using an inlet in split mode, check the split ratio.
• Check for leaks. (See “Checking for Leaks”.) To
troubleshoot small leaks in a multimode or split/splitless
inlet, see To Check for Leaks in a Split/Splitless Inlet or
To Check for Leaks in a Multimode Inlet.
• Check the inlet for contamination. (See “Contamination or
Carryover”.)
• Check each column and verify that it was cut and
installed properly at each end.
• Verify that the column type is correct.
• Perform column maintenance: Bake out contaminants,
remove the contaminated length of column near the inlet,
and reverse and bake out the column as needed.
• Verify that the liner type is appropriate for the sample.
• Verify that the detector flow settings are correct.
Measure the actual detector flows. If an actual flow does
not match the GC display, check for contamination and
restrictions, for example a plugged jet. See the following:
• To Measure a Detector Flow
• To Check for a Plugged FID Jet
• To Check for a Plugged NPD Jet
• Check the supply gas purity.
• Check all trap indicators and dates.
• Verify that the method parameters are correct.
• Some samples change with heat or ultraviolet light. Check
sample stability.
• Check configured syringe size. Some syringe sizes are
specified at half- capacity. If the maximum syringe volume
is marked at half- height on the barrel, not at the top of
the barrel, enter twice the labeled volume when
configuring the syringe size.
• If the drop in peak area or height happened gradually due
to baseline rise, rather than a sudden change, check for
detector contamination. Bakeout the detector (FID, TCD,
uECD).
If using an FID:
• Verify that the correct jet is installed.
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Chromatographic Symptoms
• Check for a dirty jet.
• Check for contaminated detector parts.
• To Perform Maintenance on the FID Collector Assembly
• To Check for a Plugged FID Jet
If using a uECD:
• Replace the fused silica indented mixing liner.
• Replace and reinstall column.
• Clean the makeup gas adapter.
If using an NPD:
• Check the detector for contamination.
• Replace ceramic insulators.
• Replace the bead.
If using an FPD:
• Verify correct column installation.
• Check that the correct filter is installed and is clean.
• Check the flow rates.
• Check the makeup gas type.
To Resolve Low Sensitivity with an FID
In normal use, the FID can develop deposits on the collector,
insulators, jet, and so forth. To reduce contamination
buildup, Agilent recommends using the detector at 300 °C or
higher. However, even with normal use deposits develop in
the jet (usually white silica from column bleed or black,
carbonaceous soot). These deposits reduce sensitivity and
cause chromatographic noise and spikes. Jets require
periodic cleaning or replacement. The following procedure
checks for causes of low sensitivity by frequency of
occurrence.
For sensitivity loss associated with noise, wander, or drift,
also see “Noisy Detector, Including Wander, Drift, and
Baseline Spikes”.
1 Check detector flow settings. See Recommended starting
conditions for new FID methods.
The general rule is 1:1 flow ratio of hydrogen to (column
+ makeup gas).
2 Measure the actual detector flow rates. See “To Measure a
Detector Flow”. If the actual hydrogen, makeup, and
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Chromatographic Symptoms
capillary column flows are lower than the display, the jet
is becoming plugged. See “To Check for a Plugged FID
Jet”. Replace the jet.
3 Check that column is properly installed. Reinstall it. See
To Install a Capillary Column in the FID. Make sure the
column is installed all the way to the tip and withdrawn
1–2 mm (column id > 100 µm).
4 Check inlet parameters that control venting, such as split
ratio and splitless purge delay time. Make sure the sample
is not being inadvertently vented.
5 Perform inlet maintenance (replace all consumable parts)
and pressure test the inlet when completed. See the
maintenance manual and “Checking for Leaks”.
6 Perform complete FID maintenance. Disassemble the FID
and clean or replace all parts. Refer to the following:
• To Perform Maintenance on the FID Collector Assembly
Agilent 7890A Troubleshooting
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Chromatographic Symptoms
FID Flame Goes Out During a Run and Attempts to Reignite
The following is an example chromatogram showing a
flameout from a large solvent peak.
pA
9
8
7
6
5
4
3
2
1
2
3
4
5
min
After a flameout, the GC will try to ignite the flame three
times. The GC tries to reignite whenever the detector output
falls below the Lit offset setpoint, regardless of whether or not
the flame was extinguished. (In a very clean system, the
baseline output may be less than 2 pA.)
If the FID flame goes out during a run, do the following:
• See if an aromatic peak or water extinguished the flame.
• Check for a plugged jet.
• Verify that the gas flow settings are correct. Verify that Lit
offset is set appropriately.
If the FID flame attempts to reignite but is already lit, do
the following:
• Verify that the FID Lit offset setting is appropriate for the
run (typically < 2.0 pA).
• Check to see if an aromatic peak or water extinguished
the flame.
• Check for a partially plugged jet. Measure actual
hydrogen, air, and makeup flows at the detector. (See “To
Measure a Detector Flow”.) Replace the jet as needed.
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3
• Check that column is properly installed. Reinstall it. See
To Install a Capillary Column in the FID. Make sure the
column is installed all the way to the tip and withdrawn
1–2 mm (column id > 100 µm).
• Check for leaks at the detector column fitting. (See
“Checking for Leaks”.)
Agilent 7890A Troubleshooting
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Chromatographic Symptoms
FID Baseline Output Above 20 pA
• Verify the purity of the carrier and detector gas supply.
See the Agilent GC, MS, and ALS Site Preparation
Checklist.
• Inspect the column for column bleed. Lower the oven
temperature to ambient. If the detector output drops
significantly, suspect a contaminated or bleeding column
or contaminated carrier gas. Confirm column bleed by
turning off column flow (with oven cool) and checking the
detector output.
• Check the gas supply trap indicators/dates and ensure
that the traps are not expended.
• Verify that the detector was reassembled properly after
recent maintenance.
• Inspect the detector for contamination. Bake out the
detector.
• Check that the FID leakage current is < 2.0 pA. (See “To
Measure FID Leakage Current”.)
• Inspect the FID flow module for contamination.
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Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
FID Baseline Output at Maximum (~8 Million)
If the FID output seems to be stuck at a very high value (up
to 8 million counts), check for a shorted collector.
1 Check if the interconnect spring has been bent. Remove
the collector assembly and visually inspect the spring.
2 Disassemble the collector assembly and visually check for
rust buildup on any parts. Replace parts as needed. To
avoid this problem, operate the detector at >300 °C.
3 Check for carbonization in the detector due to injection
or aromatic or chlorinated solvents. To avoid this
problem, operate the detector at >300 °C. Reassemble and
install the collector and operate the detector using higher
air and hydrogen flows (air must be 450 mL/min,
hydrogen at 35 mL/min). .
Agilent 7890A Troubleshooting
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3
Chromatographic Symptoms
FPD Flame Goes Out During a Run and Attempts to Reignite
If the flame goes out during a run, do the following:
• Check the GC system for leaks, especially at the detector
column fitting. (See “Checking for Leaks”.)
• Verify the detector temperature is set ≥ 200 °C.
• Ensure that condensation in the vent tube is not dripping
back into the detector. The flexible plastic vent tube must
run from the detector into a container, without sagging,
in order to properly drain water condensate. Keep the
open tube end out of the water in the container.
If the FPD flame goes out and then reignites, do the
following:
• Verify that the Lit offset setting is lower than the normal
baseline.
• Check for leaks. (See “Checking for Leaks”.)
• Check the flow settings, then measure the actual detector
flows. (See “To Measure a Detector Flow”.)
• Certain environmental conditions, such as:
• Strong electromagnetic fields
• Large ambient temperature swings
• Large atmospheric pressure swings
can cause an artificially low signal in the GC, incorrectly
indicating that the flame has gone out. As a result, the
run aborts and the GC tries to relight an already- lit
flame.
You can verify that the flame is lit by holding a cold, shiny
surface (such as a mirror or a wrench) over the exit tube.
Condensation on the surface indicates that the flame is lit.
Reset the Lit offset to 2.0.
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Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
FPD Quenching/Repeatability
Hydrocarbon quenching occurs when a high concentration of
carbon dioxide from a hydrocarbon peak is in the flame at
the same time as the sulfur species. Part of the light emitted
by the sulfur species is absorbed by some CO2 species.
Self- quenching occurs at high concentrations of the
heteroatom species. Some other ground state (inactivated)
species reabsorbs the emitted photon, preventing it from
reaching the PMT.
To resolve hydrocarbon quenching:
• The column should provide good separation of the
compounds, those that contain sulfur or phosphorus as
well as those that do not but may absorb light.
• Optimize the chromatographic separation such that
hydrocarbon peaks are resolved from sulfur or
phosphorus peaks.
1 Run the analysis first on a FID in order to see all the
peaks (the FPD ignores hydrocarbons).
2 Run the analysis on the FPD.
3 Modify the method so that the peak of interest is
separate from the rest of the peaks.
Agilent 7890A Troubleshooting
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3
Chromatographic Symptoms
FPD Output Too High or Too Low
• Verify that the correct filter is being used. Do not use a
phosphorus filter with sulfur- optimized flows or a sulfur
filter with phosphorus- optimized flows.
• Check the position of the column as installed in the
detector.
• Check the gas purity.
• Verify that the flows are optimized for the filter being
used. Monitor the FPD output. The table below provides
examples of detector output when the filter installed in
the detector and the gas flows in use do not match.
Outputs
Gas flows optimized
for
With sulfur filter
With phosphorus filter
Sulfur
30 to 50
10 to 12 (low)
Phosphorus
240 to 250 (high)
30 to 50
Besides having a mismatch between the filter installed and a
particular set of gas flows, also consider:
• If the Lit offset is 0.5 to 3.0, check that the flame is ON.
• If the Lit offset is 0, check if the electrometer is turned
OFF or the signal cable is disconnected.
• If the Lit offset <30, the flame may be in the wrong
position. Check detector flows, column flow, and column
position. See the following:
• To Measure a Column Flow
• To Measure a Detector Flow
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Chromatographic Symptoms
3
FPD Low Peak Areas
• Check the flow settings, then measure the actual detector
flows. (See “To Measure a Detector Flow”.)
• Perform complete inlet maintenance: Replace all
consumable parts and bake out the inlet.
• Perform column maintenance: Bake out contaminants,
remove the contaminated length of column near the inlet,
and reverse and bake out the column as needed.
• Verify that the column is installed properly.
• Consider the filter type (sulfur or phosphorus).
• Check the system for leaks. (See “Checking for Leaks”.)
• Verify that the method settings are appropriate.
• Check the flow rates.
• Check the makeup gas type.
Agilent 7890A Troubleshooting
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Chromatographic Symptoms
FPD Large Peak Width at Half-Height
If the FPD produces peaks that are abnormally wide at half
the peak height, do the following:
• Check the actual injection volume; reduce if necessary.
• Verify that the liner is not reacting with the sample.
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Chromatographic Symptoms
FPD Baseline Output High, > 20 pA
• Check the supply gas purity.
• Check all trap indicators and dates.
• Check the detector for contamination.
• Check for light leaks at the photomultiplier tube (PMT);
tighten the PMT if it is loose.
• Perform complete inlet maintenance: Replace all
consumable parts and bake out the inlet.
• Perform column maintenance: Bake out contaminants as
needed.
Agilent 7890A Troubleshooting
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3
Chromatographic Symptoms
FPD Chromatographic Output Showing Clipped Peaks
If you have an application at the upper limit of the dynamic
range (especially with sulfur), you may have to desensitize
your instrument. Replace the 1000- 1437 sulfur filter with
filter part number 19256- 80000. Then set the detector gas
flows to the values used in the phosphorus checkout
method. This raises the baseline but with some loss in the
signal- to- noise ratio.
There should be no problems with either solution and the
use of hydrogen. However, please note the following warning.
WA R N I N G
76
Hydrogen gas is flammable and potentially explosive. Be sure to
turn off the hydrogen gas at the source until connections are
made. Also, leak test connections, lines and valves before
operating or servicing the instrument.
Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
NPD Solvent Quenching
If the baseline does not recover after a solvent peak, try the
following:
• Turn hydrogen off/on around the solvent peak.
• Use nitrogen as the makeup gas.
• Set the total column flow and makeup gas to less than
10 mL/min.
• Increase the air flow by 10 mL/min.
• Increase the detector temperature to 325 °C.
• Implement an Agilent Dean’s switch solvent vent solution.
Agilent 7890A Troubleshooting
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Chromatographic Symptoms
NPD Response Low
• Perform complete inlet maintenance: Replace all
consumable parts and bake out the inlet.
• Perform column maintenance: Bake out contaminants as
needed. Verify correct column installation.
• A large concentration of solvent has extinguished the
hydrogen/air plasma. Increase the bead voltage. Run the
makeup gas at a flow rate of 5 mL/min.
• Verify that there is hydrogen coming from the external
supply. Check that flow and pressure are turned on at the
keyboard. The hydrogen flow rate should be between 1.0
and 5.5 mL/min. Measure the actual gas flow at the
detector. (See “To Measure a Detector Flow”.)
• Check for a partially plugged jet. See To Check for a
Plugged FID Jet.
• If the upper ceramic insulator is contaminated, a high
offset (2 to 15 pA or more) will occur when the bead is
off. This directly affects sensitivity. Replace the ceramic
insulator.
• Verify that the bead is activated. Look through the vent
hole on the detector lid to see if the bead is glowing
orange. If the bead is not glowing, check the detector
background signal. Reduce the bead voltage to zero to
establish a reference level, and then look for a sudden
sharp increase in output as the bead voltage increases,
which indicates that ignition occurred. If 4 V are being
supplied to the bead but it is not igniting, the bead is
probably burned out. Replace the bead.
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Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
• Replace the insulators/collector.
• Check for liquid phase contamination (polar phases).
Agilent 7890A Troubleshooting
79
3
Chromatographic Symptoms
NPD Baseline Output > 8 million
• The collector is shorted to the detector housing.
Disassemble the collector and insulators and reinstall.
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Agilent 7890A Troubleshooting
Chromatographic Symptoms
3
NPD Adjust Offset Process Not Functioning Properly
• Inspect the jet to see if it is clogged. (See To Check for a
Plugged NPD Jet.)
• Measure the actual detector flows. (See To Measure a
Detector Flow.) If the hydrogen or makeup flows are zero
or much lower than the displayed flow, suspect a plugged
jet.
• Check the condition of the bead. Replace if necessary.
• Verify that the flow settings are correct. See Flows,
temperatures, and bead information.
• If the process still fails, there could be a large leak in the
system. This causes measured flow rates to be different
from actual flow rates. Thoroughly leak check the whole
system, especially the detector column fitting. (See
Checking for Leaks.)
• Set the equilibration time to 0.0.
Agilent 7890A Troubleshooting
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3
Chromatographic Symptoms
NPD Low Selectivity
(High hydrocarbon response relative to nitrogen or
phosphorus.)
• Verify that the hydrogen flow is correct (< 3 mL/min).
• Inspect the bead; it may be defective or expended.
• Verify correct bead voltage.
• Replace the collector and insulators.
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Chromatographic Symptoms
3
Negative Peaks Seen with TCD
• Verify that the correct gas type is being used.
• Check for a leak in the system, especially at the detector
column fitting. (See “Checking for Leaks”.)
• Consider thermal conductivity of analytes relative to
carrier.
• Check the flow settings, then measure the actual detector
flows. (See “To Measure a Detector Flow”.)
Agilent 7890A Troubleshooting
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3
Chromatographic Symptoms
TCD Baseline Has Dampened Sinusoidal Noise Trailing Peaks (Ringing
Baseline)
Wrong data rate is selected in the data system. For TCD, the
data rate should be < 5 Hz.
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Chromatographic Symptoms
3
TCD Peaks Have Negative Dip on Tail
• Check for leaks at the detector column adapter fitting.
(See “Checking for Leaks”.)
• Upgrade the detector to a passivated filament.
Agilent 7890A Troubleshooting
85
3
86
Chromatographic Symptoms
Agilent 7890A Troubleshooting
Agilent 7890A Gas Chromatograph
Troubleshooting
4
GC Not Ready Symptoms
GC Never Becomes Ready 88
Flow Never Becomes Ready 89
Oven Temperature Never Cools Down/Cools Very Slowly 90
Oven Never Heats Up 91
Temperature Never Becomes Ready 92
Cannot Set a Flow or Pressure 93
A Gas Does Not Reach Setpoint Pressure or Flow 94
A Gas Exceeds Pressure Setpoint or Flow 95
The Inlet Pressure or Flow Fluctuates 96
Cannot Maintain a Pressure as Low as the Setpoint on a Split Inlet 97
The Measured Column Flow Does Not Equal the Displayed Flow 98
FID Does Not Ignite 99
FID Ignitor Does Not Glow During Injection Sequence 100
FID or NPD Measured Hydrogen and Makeup Gas Flows Much Less Than
Setpoint 102
NPD Adjust Offset Process Fails 103
FPD Does Not Ignite 104
Valve Not Ready 106
This section includes faults and symptoms that will occur
when the GC is on but cannot perform analyses. This is
indicated by a “Not Ready” warning, by fault messages, or by
other symptoms.
Agilent Technologies
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4
GC Not Ready Symptoms
GC Never Becomes Ready
Normally the GC becomes ready after flows and
temperatures reach setpoint. If the GC does not become
ready after a long period of time:
• Press [Status] or a component key (for example, [Front
inlet]) to see which setpoints or conditions are not ready.
• Check for a sampler problem.
• Check for a data system problem.
• If performing manual injections in splitless or gas- saver
mode, you may need to press [Prep Run] to prepare the
inlet for the injection. Do this, for example:
• To toggle the inlet purge valve before a splitless
injection
• To prepare for a pulsed injection
• To turn off gas saver.
For more information on [Prep Run], see the Agilent 7890A
GC Advanced User Guide.
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GC Not Ready Symptoms
4
Flow Never Becomes Ready
If the gas flow never becomes ready, check for the following:
• Check the supply gas for sufficient delivery pressure.
• Check the restrictors installed in the Aux EPC module.
See Restrictors in the Advanced User Guide.
• Check the configured gas type. The configured gas type
must match the actual gas plumbed to the GC.
• Check for leaks in the gas delivery plumbing and the GC.
(See “Checking for Leaks”.)
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GC Not Ready Symptoms
Oven Temperature Never Cools Down/Cools Very Slowly
If the oven does not cool down or cools down very slowly:
WA R N I N G
The exhaust coming from the back of the GC is very hot. Keep
hands and face away from the exhaust vent.
• Check oven flapper operation.
1 Decrease oven temperature by at least 20 degrees.
2 Verify that the oven flaps in the back of the GC are
open. Listen to verify that the fan is operating. The
figure below illustrates the location of the two oven
flaps.
If the flaps are not operating smoothly, contact Agilent
for service.
If using cryo cooling:
• Check for sufficient cryo coolant.
• Check if operating limits have been exceeded.
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GC Not Ready Symptoms
4
Oven Never Heats Up
• Press [Status] to check for errors to report to Agilent.
WA R N I N G
The exhaust coming from the back of the GC is very hot. Keep
hands and face away from the exhaust vent.
• Power cycle the GC.
• Check oven flapper operation.
1 Increase oven temperature by at least 20 degrees.
2 Verify that the oven flaps in the back of the GC are
closed. The figure below illustrates the location of the
two oven flaps.
If the flap is stuck open or if the flaps are closed and the
oven still does not heat, contact Agilent.
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4
GC Not Ready Symptoms
Temperature Never Becomes Ready
To be considered ready, a temperature must be at setpoint
±1 °C for 30 s. If a temperature never becomes ready, do the
following:
• Check for a missing insulation cup on an inlet or
detector.
• Check for a very large temperature difference between the
oven and inlet or detector.
• Check for missing insulation around the inlet or detector.
• If using a cool on- column with CryoBlast or a PTV or
MMI inlet:
• Check cryo coolant level.
• Check if operating limits have been exceeded. If, for
example, you are operating the GC in a hot room at a
high oven temperature and a very low inlet
temperature, an inlet may not reach its desired
temperature.
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GC Not Ready Symptoms
4
Cannot Set a Flow or Pressure
If you cannot set a flow or pressure using the split/splitless,
MMI, PTV, VI, or cool on- column inlets, do the following:
• Check the column mode.
• Check that a capillary column is configured to the correct
inlet.
• Check the configured column dimensions.
• Check that the flow is turned on.
If you cannot set a flow or pressure using the purged packed
inlet, do the following:
• Check the column mode.
• Check that the flow is turned on.
• Check the inlet mode. When using inlet flow control, you
can set only flow control modes for columns. When using
inlet pressure control, you can set the column for both
flow and pressure modes.
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GC Not Ready Symptoms
A Gas Does Not Reach Setpoint Pressure or Flow
If an inlet does not reach its pressure setpoint, it will shut
down in an amount of time determined by the type of inlet.
Do the following:
• Check for sufficient gas supply delivery pressure. The
pressure at the supply should be at least 10 psi greater
than the desired setpoint.
• Check for leaks. (See “Checking for Leaks”.) A large leak
may be present somewhere in the system. Use an
electronic leak detector to find leaks, then correct them.
Do not forget to check the column—a broken column is a
very large leak.
• To troubleshoot a multimode or split/splitless inlet, see
“To Check for Leaks in a Multimode Inlet” or “To Check
for Leaks in a Split/Splitless Inlet”.
• If using gas saver, be sure that the gas saver flow rate is
high enough to maintain the highest column- head
pressure used during a run.
• Check for an incorrectly installed column.
• Check for a defective inlet or detector pressure sensor.
If you are using a split/splitless inlet, MMI inlet, PTV inlet,
or volatiles interface:
• Check the split ratio. Increase the amount of split flow.
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GC Not Ready Symptoms
4
A Gas Exceeds Pressure Setpoint or Flow
If a gas exceeds its pressure or flow setpoint, do the
following:
If using a split/splitless inlet, MMI inlet, PTV inlet, or
volatiles interface:
• Decrease the split ratio.
• Replace the split vent filter. See the procedure for the SS,
MMI, PTV, or VI.
• Check the split vent trap line for contamination or an
abnormal restriction. Run the split vent restriction test in
Agilent Instrument Utilities, if available, or from the GC
front panel. See:
• To Check or Monitor Split Vent Line Backpressure
• To Run the Inlet Trap Check
• To Check a Split Vent Line for Contamination
• Verify that the correct liner is selected (if liner is used).
See Selecting the correct MMI inlet liner or Selecting the
correct SS inlet liner.
• Verify the method pressure settings for the SS inlet are
above the minimum viable settings available on the GC.
See Table 4.
• Check the gold seal for contamination (for split/splitless
inlet). See To Replace the Gold Seal on the Split/Splitless
Inlet.
• For a split/splitless inlet, if using a liner that causes a
restriction, install a high flow gold seal.
If using an FID or NPD:
• Check for a plugged jet. See “To Check for a Plugged FID
Jet” or “To Check for a Plugged NPD Jet”.
Valves:
• Check for a misaligned rotor. Align the rotor.
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GC Not Ready Symptoms
The Inlet Pressure or Flow Fluctuates
A fluctuation in inlet pressure causes variations in the flow
rate and retention times during a run. Do the following:
• Check if the gas purifier or gas generator is operating at
or near capacity.
• Check the supply gas for sufficient delivery pressure.
• Verify that the supply pressure regulator is functioning
properly. Systems with long supply tubing lengths may
require a step- down regulator near the GC. Also, use an
additional regulator to smooth out fluctuations caused by
gas generators.
• Check for leaks. (See “Checking for Leaks”.) A large leak
may be present somewhere in the system. Use an
electronic leak detector to find leaks, then correct them.
Do not forget to check the column—a broken column is a
very large leak.
• Check for large restrictions in the inlet liner or split vent
trap.
• Verify that the correct liner is installed. Some liners have
large pressure drops caused by design or tight packaging.
• Check for extreme changes in room temperature during
runs. Correct laboratory temperature problem or move the
instrument to a more suitable location.
• Check for a restriction in headspace, purge and trap, and
any other external sampling devices.
• Verify Auto Flow Zero feature is On. See AutoFlowZero.
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GC Not Ready Symptoms
4
Cannot Maintain a Pressure as Low as the Setpoint on a Split Inlet
If the GC cannot maintain a pressure as low as the setpoint,
check for the following:
• Consider using a liner designed for split analysis.
• Method pressure parameter (or resultant pressure from a
flow setting) is too low for the carrier gas type. See
Split/Splitless inlet split mode minimum operating
pressures or Multimode inlet split mode minimum
operating pressures and the table below.
Table 4
Approximate minimum viable inlet pressures for inlet in split mode, in psi (split/splitless, multimode)
Split vent flow (mL/min)
50–100
100–200
200–400
400–600
Split liners - 5183-4647, 19251-60540
2.5
3.5
4.5
6.0
Splitless liners - 5062-3587, 5181-8818
4.0
5.5
8.0
11.0
Split liners - 19251-60540, 5183-4647
3.0
4.0
—
—
Splitless liners - 5062-3587, 5181-8818
4.0
6.0
—
—
Helium and hydrogen carrier gases
Nitrogen carrier gas
• Check for a plugged liner.
• Check for contamination or restriction in the split vent
line. See:
• To Perform a SS Split Vent Restriction Test.
• To Check or Monitor Split Vent Line Backpressure
• To Run the Inlet Trap Check
• To Check a Split Vent Line for Contamination
• For the split/splitless inlet, replace gold seal..See To
Replace the Gold Seal on the Split/Splitless Inlet.
Agilent 7890A Troubleshooting
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GC Not Ready Symptoms
The Measured Column Flow Does Not Equal the Displayed Flow
If the actual column flow does not match the calculated flow
displayed on the GC within 10%, do the following:
• Verify that the measured flows are corrected to 25 °C and
1 atmosphere.
• Verify that the correct column dimensions are configured
accurately, including the actual (trimmed) column length.
• A short (<15 m) 0.58 to 0.75 mm id WCOT column is
being used with a split/splitless capillary inlet. The total
flow controller is set for a high flow rate, which creates
some pressure in the inlet and causes column flow even
with a setpoint pressure of zero. (In these situations, an
actual pressure may be shown on the display, even with a
zero setpoint.) With short, 530 to 750 mm columns, keep
the total flow rate as low as possible (for example, 20 to
30 mL/min). Install a longer column with higher
resistance (for example, 15 to 30 m).
• The split vent line or trap may be partly plugged, creating
an actual inlet pressure higher than the setpoint pressure.
Check for a restriction in the split vent line. See To Run
the Inlet Trap Check.
• If using a Mass Selective Detector, verify the column
outlet for the transfer line is set to MSD.
• Make sure that the auto flow zero is turned on. As
applicable, zero the flow and pressure sensor for the flow
module. If this does not solve the problem, replace the
flow module.
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GC Not Ready Symptoms
FID Does Not Ignite
• Verify that the Lit Offset is < 2.0 pA.
• Ensure that the FID temperature is high enough for
ignition (>150 °C). Agilent recommends >300 °C.
• Check that the FID ignitor glows during ignition sequence.
(See To Verify FID Ignitor Function During Ignition
Sequence.)
• Check that the air and hydrogen pressures meet Agilent’s
recommendations (hydrogen > 35 psi [210 kPa] and air >
55 psi [380 kPa]). See the Agilent GC, MS, and ALS Site
Preparation Checklist.
• Try increasing the supply pressures to the FID flow
module. This makes the flame easier to light without
changing the setpoints.
• Increase hydrogen and air flow rates until ignition occurs,
then reduce them toward the method values. Experiment
for the best values.
• Check for a plugged or partially plugged jet. (See To
Check for a Plugged FID Jet.)
• Check the FID flow rates. Actual flow rates should be
within +/- 10% of the setpoint. (See FID starting
conditions.) The hydrogen:air ratio greatly impacts
ignition. Nonoptimal flow settings can prevent flame
ignition. (See To Measure a Detector Flow.)
• There could be a large leak in the system if the flame still
will not light. Large leaks result in measured flow rates
being different from actual flow rates, causing nonideal
ignition conditions. Thoroughly leak check the whole
system, especially the column fitting at the FID. (See
Checking for Leaks).
• Check the column flow rate. (See To Measure a Column
Flow.) Hydrogen flow should be greater than the sum of
the column flow and makeup flow.
• If the analysis permits, substitute nitrogen for helium as
makeup.
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GC Not Ready Symptoms
FID Ignitor Does Not Glow During Injection Sequence
WA R N I N G
Keep body parts at a safe distance from the FID chimney while
performing this task. If using hydrogen, the FID flame will not be
visible.
1 Remove the detector top cover.
2 Turn the FID flame On.
3 Observe the ignitor plug though the FID chimney. The
small hole should glow during ignition sequence.
If the test fails, check for the following possible causes:
• The ignitor may be bad; replace the ignitor. (See To
Perform Maintenance on the FID Collector Assembly.)
• Detector temperature is set to < 150 °C. Agilent
recommends operating the FID at > 300 °C.
• The ignitor is not making a good connection to the
ground:
• The ignitor must be tightly screwed into the FID castle
assembly.
• The three T- 20 Torx screws that hold the collector
assembly in place must be tight.
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GC Not Ready Symptoms
• The brass knurled nut that holds the FID castle
assembly in place must be tight.
Perform FID maintenance if these parts are corroded or
oxidized.
T-20 Torx screws (3)
Ignitor
Knurled nut
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GC Not Ready Symptoms
FID or NPD Measured Hydrogen and Makeup Gas Flows Much Less Than
Setpoint
• Check for a clogged or partially clogged jet. A clogged jet
creates backpressure. Since the flow module uses pressure
control, the increased backpressure simulates proper flow.
The actual flow rate will drop but the GC remains
functional. See:
“To Check for a Plugged FID Jet”
“To Check for a Plugged NPD Jet”
• Check for a column fitting leak at the detector base.
• Replace the FID or NPD jet.
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GC Not Ready Symptoms
4
NPD Adjust Offset Process Fails
• Inspect the jet to see if it is clogged. (See To Check for a
Plugged NPD Jet.)
• Measure the actual detector flows. (See To Measure a
Detector Flow.) If the hydrogen or makeup flows are zero
or much lower than the displayed flow, suspect a plugged
jet.
• Check the condition of the bead. Replace if necessary.
• Verify that the flow settings are correct. See Flows,
temperatures, and bead information.
• If the process still fails, there could be a large leak in the
system. This causes measured flow rates to be different
from actual flow rates. Thoroughly leak check the whole
system, especially the detector column fitting. (See
Checking for Leaks.)
• Set the equilibration time to 0.0.
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GC Not Ready Symptoms
FPD Does Not Ignite
• Check that the FPD temperature is high enough for
ignition (> 150 °C).
• Check FPD flow rates and that they match the type of
filter installed in the FPD. The hydrogen:air ratio greatly
impacts ignition. Nonoptimal flow settings can prevent
flame ignition.
Table 5
FPD recommended flows
Sulfur mode flows,
mL/min
Phosphorus mode
flows, mL/min
Carrier (hydrogen, helium, nitrogen, argon)
Packed columns
10 to 60
10 to 60
Capillary columns
1 to 5
1 to 5
Hydrogen
50
75
Air
60
100
Carrier + makeup
60
60
Detector gases
• Measure the actual detector flows. (See To Measure a
Detector Flow.)
• The column may be installed too high into the detector.
• Check that the FPD ignitor operates. (See To Verify That
the FPD Flame Is Lit.)
• During the ignition sequence, display the air flow rate.
The air flow rate should go to 200 mL/min while trying
to ignite to flame. If not, there is insufficient supply
pressure.
• Check the column and makeup flow rates.
• Ensure that condensation in the vent tube is not dripping
back into the detector. The flexible plastic vent tube must
run from the detector into a container, without sagging,
in order to properly drain water condensate. Keep the
open tube end out of the water in the container.
• Check the Lit offset value. The typical Lit offset value is 2.0.
If it is zero, autoignition is turned off. If it is too large,
the software will not recognize that the flame is lit and
will shut the detector down.
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GC Not Ready Symptoms
• If the flame still will not light, there could be a large leak
in the system. This results in measured flow rates being
different from actual flow rates, causing non- ideal ignition
conditions. Thoroughly leak check the whole system. (See
Checking for Leaks.)
• Try increasing the supply pressures to the FPD flow
module. This makes the flame easier to light without
changing the setpoints.
• Under some operating conditions, the flame may be more
easily lit with the rubber drip tube removed. After
lighting the flame, reinstall the drip tube.
• The sulfur mode can be particularly hard to light. Try
changing to the phosphorus mode flows, lighting the
flame, and gradually alter the flows to the sulfur values.
• Check cable connections to coupling, coupling connection
to glow plug, tight glow plug.
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GC Not Ready Symptoms
Valve Not Ready
Troubleshooting depends on the type of valve.
External valves
External valves are valves connected to the GC through the
external events or BCD connectors on the back panel
This Not Ready state means that the +24 V supply to the
pneumatics valves is actually less than +16.5 V. All valves
are disabled to prevent improper operation.
When full voltage is restored, the GC becomes ready.
This Not Ready state could indicate a hardware problem in
the external valve or in the GC analog and power board.
Gas sampling valves
The GC is normally not ready whenever the inject time or
load time has not elapsed. It becomes ready when the
specified load or inject time has passed.
Multiposition valve
A multiposition valve can cause the GC to be in a not ready
state for one of the following reasons:
• The multiposition valve is not at the setpoint position.
The GC remains not ready until the valve reaches the
setpoint.
• The BCD cable is missing or not plugged into the
receptacle. If the cable is missing, the valve will never
become ready.
• The BCD setpoint is incorrect for the valve BCD output
polarity. The valve will most likely shutdown with Illegal
Position or Not Switching shutdown errors.
• If the valve is plugged or the sample is viscous, the
switching time may be too short for the valve to switch.
Increase the switching time.
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Agilent 7890A Gas Chromatograph
Troubleshooting
5
Shutdown Symptoms
Column Shutdowns 108
Hydrogen Shutdowns 110
Thermal Shutdowns 112
Agilent Technologies
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5
Shutdown Symptoms
Column Shutdowns
The GC monitors inlet and auxiliary gas streams. If a carrier
gas (which can include an auxiliary flow module or
pneumatics control module) is unable to reach its flow or
pressure setpoint, the GC assumes that a leak exists. It will
warn you with a beep after 25 seconds, and it will continue
to beep in intervals. After about 5 minutes, the GC will shut
down components to create a safe state. The GC:
• Displays Front inlet pressure shutdown.
• Turns off to avoid column damage.
• Opens oven flaps in the back of the oven halfway.
• Flashes oven temperature setpoint Off.
• Turns off all flows for the column. When viewed, their
parameters flash Off. For example, the septum purge and
column flows for a split/splitless inlet would turn off.
• Turns off all other heaters. When viewed, their
temperature parameters flash Off.
• Attempts to turn on a shut- down zone fail with an error
message.
• Turns off the TCD filament.
• Turns off the FID or FPD ignitor, and the air and fuel gas
flows.
• Turns off the NPD bead, and air and fuel gas flows.
To recover from this state.
1 Fix the cause of the shutdown. Verify the carrier gas
supply. The GC requires a delivered gas pressure of 70
kPa (10 psi) higher than the highest pressure used in the
run. See the Agilent GC, MS, and ALS Site Preparation
Checklist.
• Check for a broken column near the inlet.
• Check for leaks.
• Replace the inlet septum.
• Replace the inlet O- ring.
• Check the supply pressure.
2 Press the key for the device that initiated the shutdown.
Scroll to the pneumatic parameter that is flashing Off,
then press [On] or [Off].
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Shutdown Symptoms
For example, if the front inlet ran out of carrier gas,
press [Front Inlet], scroll to the pressure or flow parameter,
then press [On].
• After a column shutdown, you can turn on a detector
gas flow even if the keyboard is locked by a data
system.
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Shutdown Symptoms
Hydrogen Shutdowns
Hydrogen gas may be used as a carrier or as fuel for some
detectors. When mixed with air, hydrogen can form explosive
mixtures.
The GC monitors inlet and auxiliary gas streams. If a stream
is unable to reach its flow or pressure setpoint and if that
stream is configured to use hydrogen, the GC assumes that a
leak exists. It will warn you with a beep after 25 seconds,
and it will continue to beep in intervals. After about 5
minutes, the GC will shut down components to create a safe
state. The GC:
• Displays Hydrogen Safety Shutdown.
• Closes the carrier supply valve to the inlet and closes and
turns off both pressure and flow controls. When viewed,
these parameters will flash Off.
• Opens the split vent valves in the split/splitless and PTV
inlets.
• Turns off the oven heater and fan and opens the oven
flaps.
• Turns off all heaters (including any devices connected to
the auxiliary heater controls, such as valve box heaters
and transfer line heaters). When viewed, these parameters
will flash Off.
• Turns off the TCD filament.
• Turns off the FID or FPD ignitor, and the air and fuel gas
flows.
• Turns off the NPD bead, and air and fuel gas flows.
• Sounds an alarm.
WA R N I N G
The GC cannot detect leaks in the detector gas streams. For this
reason, it is vital that the column fittings of the FID, NPD, and any
other detectors that use hydrogen always be connected to a
column or have a cap or plug installed and that hydrogen streams
be configured so that the GC is aware of them.
To recover from a hydrogen shutdown state:
1 Fix the cause of the shutdown:
• Replace the inlet septum. See the Maintenance manual.
• Replace the inlet O- ring. See the Maintenance manual.
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Shutdown Symptoms
• Check for broken column.
• Check the supply pressure. Make sure the gas supply
meets the pressure recommendations listed in the
Agilent GC, MS, and ALS Site Preparation Checklist.
• Check the system for leaks. See Leak Check Tips.
2 Power cycle the GC.
3 After the GC powers back on, press the key for the device
that initiated the shutdown. Scroll to the pneumatic
parameter that is flashing Off, then press [On] or [Off]. For
example, if the front inlet ran out of carrier gas, press
[Front Inlet], scroll to the pressure or flow parameter, then
press [On].
• After a column shutdown, you can turn on a detector
gas flow even if the keyboard is locked by a data
system.
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Shutdown Symptoms
Thermal Shutdowns
A thermal fault means that the oven or another heated zone
is not within its allowable temperature range (lower than
minimum temperature or higher than maximum
temperature). Several things could cause this error:
• A problem with the electrical supply to the instrument.
• A malfunction of the zone control electronics.
• A shorted temperature sensor.
• A shorted heater.
To recover from this state:
1 Fix the cause of the shutdown:
• Check for missing insulation.
2 Most thermal shutdowns can be cleared by shutting off
the thermal zone.
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Agilent 7890A Gas Chromatograph
Troubleshooting
6
GC Power On and Communication
Symptoms
GC Does Not Turn On 114
PC Cannot Communicate with GC 115
GC Does Not Recover After Firmware Update 116
GC Turns On, Then Stops During Startup (During Self-Test) 117
Agilent Technologies
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GC Power On and Communication Symptoms
GC Does Not Turn On
If the GC does not turn on:
• Check the power cord.
• Check the building’s power.
• If the problem is at the GC, turn off the GC power. Wait
30 seconds, then turn the on the GC power.
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GC Power On and Communication Symptoms
6
PC Cannot Communicate with GC
• Run a ping test
The MS- DOS ping command verifies communications
across a TCP/IP connection. To use it, open the command
prompt window. Type ping followed by an IP address. For
example, if the IP address is 10.1.1.101, enter ping
10.1.1.101. If LAN communications are working properly,
you will see a successful reply. For example:
If the ping test is successful, check the software
configuration.
If the problem is that a data system cannot connect to the
GC, check if another PC is controlling the GC. At the GC
keypad, press [Options], scroll to and select Communication,
then scroll the display down. If a computer is connected to
the GC, its network name will appear below the Enable DHCP
line.
If the ping test is unsuccessful, do the following:
• Check the LAN cabling.
• Verify the IP address, subnet mask, and gateway
addresses.
• Make sure all network devices (hubs, switches, and so
forth) are turned on, properly connected, and working.
• Check for a defective LAN card in the PC.
• If using a direct PC to GC setup, make sure you are using
a crossover cable. If using a setup with a hub or switch
(that is, connecting to a building or site LAN), make sure
you are NOT using a crossover cable.
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GC Power On and Communication Symptoms
GC Does Not Recover After Firmware Update
If the GC starts but does not display the “Power on
successful” message, look for any error messages. Record any
messages. Then resolve the problem as follows:
1 Try power cycling the GC.
2 If the GC still does not recover, turn off the GC.
3 While pressing the [Stop] and [0] keys, turn on the GC.
Continue to hold the keys until the GC reboots. You
should see a display similar to the following:
MMON Version X.XX
IP = 10. 1. 1.101
If this display appears, you can now communicate to the
GC. Reload the firmware.
4 If the GC does not boot up and show a display similar to
the one above, or if the update fails again, contact Agilent
for service.
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GC Power On and Communication Symptoms
GC Turns On, Then Stops During Startup (During Self-Test)
If the GC turns on but the normal display does not appear:
1 Turn the GC power switch Off. Wait one minute, then turn
the GC power On.
2 If the GC does not return to normal, record any messages
that appear on the display. Observe the GC back panel,
and look for LED indicator lights (green, yellow, or red)
above the REMOTE connector and whether they are
flashing or constant. (For older GCs, look through the
slots in the GC right side panel where shown below.)
Contact Agilent for service, and provide the display
information to the Agilent support personnel. (See also
“Information to Obtain Before Calling Agilent for
Service”.)
Older GC: LEDs visible through side panel.
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118
GC Power On and Communication Symptoms
Agilent 7890A Troubleshooting
Agilent 7890A Gas Chromatograph
Troubleshooting
7
Checking for Leaks
Leak Check Tips 120
To Check for External Leaks 121
To Check for GC Leaks 123
Leaks in Capillary Flow Fittings 124
To Perform an Inlet Leak Check 125
To Check for Leaks in a Split/Splitless Inlet 128
To Perform a SS Pressure Decay Leak Test 130
To Check for Leaks in a Multimode Inlet 131
To Perform a MMI Pressure Decay Test 133
To Perform a PP Pressure Decay Leak Test 134
To Perform a COC Pressure Decay Leak Test 135
To Perform a PTV Pressure Decay Test 136
To Perform a VI Pressure Decay Test 137
Agilent Technologies
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Checking for Leaks
Leak Check Tips
When checking for leaks, consider the system in two parts:
external leak points and GC leak points.
• External leak points include the gas cylinder (or gas
purifier), regulator and its fittings, supply shutoff valves,
and connections to the GC supply fittings.
• GC leak points include inlets, detectors, column
connections, valve connections, and connections between
flow modules and inlets/detectors.
WA R N I N G
Hydrogen (H2) is flammable and is an explosion hazard when
mixed with air in an enclosed space (for example, a flow meter).
Purge flowmeters with inert gas as needed. Always measure
gases individually. Always turn off detectors to prevent
flame/bead autoignition.
WA R N I N G
Hazardous sample gases may be present.
1 Gather the following:
• Electronic leak detector capable of detecting the gas
type
• 7/16- in, 9/16- in, and 1/4- in wrenches for tightening
Swagelok and column fittings
2 Check any potential leak points associated with any
maintenance recently performed.
3 Check GC fittings and connections that undergo thermal
cycling, since thermal cycling tends to loosen some fitting
types. Use the electronic leak detector to determine if a
fitting is leaking.
• Start by checking any newly made connections first.
• Remember to check connections in the gas supply lines
after changing traps or supply cylinders.
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Checking for Leaks
7
To Check for External Leaks
Check for leaks at these connections:
• Gas supply bulkhead fittings
• Gas cylinder fitting
• Regulator fittings
• Traps
• Shut- off valves
• T- fittings
Perform a pressure drop test.
1 Turn off the GC.
2 Set the regulator pressure to 415 kPa (60 psi).
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Checking for Leaks
3 Fully turn the regulator pressure adjustment knob
counterclockwise to shut the valve.
4 Wait 5 min. If there is a measurable drop in pressure,
there is a leak in the external connections. No drop in
pressure indicates that the external connections are not
leaking.
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Checking for Leaks
To Check for GC Leaks
Check for leaks at these connections:
• Inlet septum, septum head, liner, split vent trap, split vent
trap line, and purge vent fittings
• Column connections to inlets, detectors, valves, splitters,
and unions
• Fittings from the flow modules to the inlets, detectors,
and valves
• Column adapters
• Agilent capillary flow fittings
First, use the GC’s built- in leak test to check for leaks at the
inlet column fitting, septum, liner, split vent trap line, and
so forth. See “To Perform an Inlet Leak Check”. Correct any
leaks found using this test. If the GC still shows symptoms
of a leak, check the other possible leak points.
If using Agilent Instrument Utilities, you can also use it to
remotely run an inlet leak check (for selected inlet types).
If the inlet passes the inlet leak check but you still suspect a
leak in the inlet, you can use the Instrument Utilities
software to perform a pressure decay test for most inlets.
(You can also perform a manual pressure decay test on any
inlet.) Any inlet that passes the inlet pressure decay test can
be considered leak free.
• To Perform a SS Pressure Decay Leak Test
• To Perform a MMI Pressure Decay Test
• To Perform a PP Pressure Decay Leak Test
• To Perform a COC Pressure Decay Leak Test
• To Perform a PTV Pressure Decay Test
• To Perform a VI Pressure Decay Test
Use an electronic leak detector to check column connections
and tubing connections. See also:
• To Check for Leaks in a Split/Splitless Inlet
• To Check for Leaks in a Multimode Inlet
• Leaks in Capillary Flow Fittings
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Checking for Leaks
Leaks in Capillary Flow Fittings
For capillary flow fittings, a leak usually indicates that the
fitting has been overtightened. Unless the fitting is obviously
loose, do not tighten it further. Instead, remove the
connection, trim the column end, and install it again. (See
To Attach a Capillary Column Using SilTite Metal Fittings.)
Also inspect the plate and connection for a broken column
tip.
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Checking for Leaks
7
To Perform an Inlet Leak Check
The GC provides a real- time, built- in leak check for all
inlets. This check is most useful for finding inlet leaks
during and after inlet maintenance. While not as thorough or
sensitive as a complete inlet pressure test, it is normally
performed with the column installed and configured, and
provides a quick assurance that the inlet is reasonably
leak- free. Agilent recommends running the check before and
during inlet maintenance, so that as you tighten any fittings
you can watch the inlet stop leaking. The test is appropriate
for all applications, although some may require more robust
leak testing.
The inlet leak check finds leaks at the:
• Inlet column fitting
• Gold seal (as applicable)
• Split vent trap housing (as applicable)
• Septum nut and septum (as applicable)
• Insert weldment nut/septum head assembly (as applicable)
To run the test:
1 At the GC keypad, press [Service Mode], scroll to Front inlet
leak check or Back inlet leak check, then press [Enter].
2 The display will be similar to Figure 4:
FRONT INLET LEAK CHECK
TotalFlow
1.74
Col
1.34<
Test Inlet
(ON to Start)
Test pressure
10.0 psi
Warning if check flow
OFF
Fault if check flow
OFF
Last test results
Tue Oct 20 16:07 2009
Test flow OK:
4.8
Reset the test results? (yes)
Figure 4
Agilent 7890A Troubleshooting
Example front inlet leak check display. Example assumes a test
has been previously run. (Scroll the display to see all lines.)
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7
Checking for Leaks
3 Verify that the Test pressure is acceptable. Typically, the
default pressure of 10 psi works well. If desired, enter a
different inlet pressure.
• For repeatable results, use the same value for the same
hardware.
• Enter a higher test pressure if using a column that
produces high backpressure.
4 Scroll to Test Inlet and press [On/Yes].
5 After a moment, the test stabilizes.
• The TotalFlow reading shows the total flow of carrier
gas through the inlet. The Col reading shows the flow
through the column.
• The approximate leak rate is TotalFlow – Col, in mL/min.
• Consider the inlet leak free if the Col reading
approximately equals the TotalFlow reading.
6 While monitoring the readings, tighten fittings, replace the
septum, change the liner O- ring, and so forth as needed.
If the repair stops the leak, you will see the Col reading
decrease to be approximately equal to the TotalFlow
reading.
NOTE
If you ran the test on a leak-free inlet before performing maintenance, the
leak test result after maintenance should be about the same as it was
before maintenance.
7 If the test still fails:
• Replace the septum
• Reinstall the column into the inlet
• Replace the liner and liner O- ring
• Open the split vent trap and check the O- ring seating.
Replace the split vent trap if needed.
If the test passes, but you still suspect an inlet leak, perform
a pressure decay leak test. See:
• To Perform a SS Pressure Decay Leak Test
• To Perform a MMI Pressure Decay Test
• To Perform a PP Pressure Decay Leak Test
• To Perform a PTV Pressure Decay Test
• To Perform a VI Pressure Decay Test
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To set warning limits for a leak check
The GC provides two alerts related to the inlet leak check:
• Warning if pressure check: If the measured pressure exceeds
the limit, turn on the Service Due indicator.
• Fault if pressure check: If the measured pressure exceeds the
limit, make the GC Not Ready.
You can determine reasonable inlet leak check results, then
set the GC to either go Not Ready or set the Service Due
indicator if the leak check fails. To set one or both limits:
1 When the inlet is considered leak- free, run the inlet leak
check. (Assume the inlet is leak- free if the TotalFlow and
Col readings are very close and you are satisfied with the
GC’s chromatographic results.)
2 Note the TotalFlow result.
3 Scroll to Warning if pressure check or Fault if pressure check.
4 Enter a limit using the keypad, then press [Enter].
• Select a flow rate that is higher than the acceptable
TotalFlow reading. Ideally, enter a value that
corresponds to known chromatographic problems.
• The warning and fault limits can be different, for
example, a warning at a lower limit, and a fault at a
higher one.
5 If desired, repeat for Fault if pressure check.
6 The test is now set up.
7 Periodically rerun the test. When the test fails, fix any
leaks.
To clear a Not Ready condition or to turn off the Service
Due indicator:
1 Press [Service Mode], scroll to Front inlet leak check or Back
inlet leak check, then press [Enter].
2 Scroll to Reset the test results? and press [On/Yes].
To disable a warning limit for the inlet leak check
1 Press [Service Mode], scroll to Front inlet leak check or Back
inlet leak check, then press [Enter].
2 Scroll to the warning limit, then press [Off/No].
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Checking for Leaks
To Check for Leaks in a Split/Splitless Inlet
This procedures describes how to check for and fix leaks in
the split/splitless inlet. Follow the procedures below based
on the inlet’s symptoms.
Cannot Reach Pressure Setpoint
If the split/splitless EPC inlet does not reach its pressure
setpoint, the GC will be “Not Ready.” Pressing [Status]
indicates the front (or back) inlet pressure is not ready. The
GC will shut down in approximately 5.5 minutes if the inlet
cannot pressurize and control.
If you have recently performed maintenance, first check for
leaks on any fittings/parts you handled.
1 Verify sufficient gas supply pressure delivered to the GC
(see the GC, MS, and ALS Site Preparation Checklist), and
verify no leaks in the gas supply (see To Check for
External Leaks). The inlet requires 70 kPa (10 psi) above
the highest pressure used in the method.
• 120 psi maximum for 0–100 psi inlet
• 170 psi maximum for 0–150 psi inlet
2 Check the total flow setting. Total flow must be high
enough to maintain inlet pressure throughout the run.
Wide bore columns require higher flow rates. Typically
50 mL/min is sufficient. To increase total flow:
• Increase split ratio if in split mode
• Increase the purge flow for splitless mode
3 Put your thumb (or a septum) over the split vent exhaust.
If the inlet pressure begins to rise to the setpoint, call
Agilent for service. If the pressure remains low, continue
with the next step.
4 Perform the inlet run leak check. See “To Perform an
Inlet Leak Check”. The total flow provides an indication
of the magnitude of the leak. Monitor the total flow while
checking/tightening fittings:
• Septum nut
• Column
• Split vent trap/O- rings
• Liner/O- rings
• Gold seal
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Checking for Leaks
• Split vent line connection to the inlet body
• Flow block fittings on the flow manifold
Alternately, use an electronic leak detector to check these
fittings/connections.
If these checks do not resolve the problem, contact
Agilent for service.
Low Sensitivity or Poor Repeatability
A small leak in the split/splitless EPC inlet can cause low
sensitivity or poor repeatability. Check for and isolate a
small leak as described below.
If you have recently performed maintenance, first check for
leaks on any fittings/parts you handled.
1 Perform the inlet pressure decay test. See “To Perform a
SS Pressure Decay Leak Test”. If the test passes, consider
the inlet leak- free and check other possible causes for the
low sensitivity or poor repeatability.
2 If the pressure decay test fails, perform the inlet leak
check. See “To Perform an Inlet Leak Check”. Monitor the
total flow while checking/tightening fittings:
• Septum nut
• Column
• Split vent trap
• Liner/O- ring
• Gold seal
• Split vent line connection to the inlet body
• Flow block fittings on the flow manifold
3 If the inlet (prep run) leak check did not resolve the
problem, the leak may be too small to detect using that
test. Use an electronic leak detector to check the
fittings/connections.
If these checks do not resolve the problem, contact Agilent
for service.
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Checking for Leaks
To Perform a SS Pressure Decay Leak Test
Use the Agilent Instrument Utilities Split/Splitless Inlet
Pressure Decay Test to determine if the inlet is leaking.
Open the software, select the GC, and run the test for the
inlet. See To Perform an Inlet Leak Check and To Perform a
SS Split Vent Restriction Test.
If the Instrument Utilities software is not available, refer to
the procedure described in the Advanced User Guide.
If the test fails:
• See “To Check for Leaks in a Split/Splitless Inlet”.
• Check the plugged column fitting and septum purge cap.
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Checking for Leaks
To Check for Leaks in a Multimode Inlet
This procedures describes how to check for and fix leaks in
the Multimode inlet. Follow the procedures below based on
the inlet’s symptoms.
Cannot Reach Pressure Setpoint
If the Multimode EPC inlet does not reach its pressure
setpoint, the GC will be “Not Ready.” Pressing [Status]
indicates the front (or back) inlet pressure is not ready. The
GC will shut down in approximately 5.5 minutes if the inlet
cannot pressurize and control.
If you have recently performed maintenance, first check for
leaks on any fittings/parts you handled.
1 Verify sufficient gas supply pressure delivered to the GC
(see the GC, MS, and ALS Site Preparation Checklist), and
verify no leaks in the gas supply (see To Check for
External Leaks). The inlet requires 70 kPa (10 psi) above
the highest pressure used in the method.
• 120 psi maximum for 0–100 psi inlet
• 170 psi maximum for 0–150 psi inlet
2 Check the total flow setting. Total flow must be high
enough to maintain inlet pressure throughout the run.
Wide bore columns require higher flow rates. Typically
50 mL/min is sufficient. To increase total flow:
• Increase split ratio if in split mode
• Increase the purge flow for splitless mode
3 Put your thumb (or a septum) over the split vent exhaust.
If the inlet pressure begins to rise to the setpoint, call
Agilent for service. If the pressure remains low, continue
with the next step.
4 Perform the inlet leak check. See “To Perform an Inlet
Leak Check”. The total flow provides an indication of the
magnitude of the leak. Monitor the total flow while
checking/tightening fittings:
• Septum nut
• Column
• Split vent trap/O- rings
• Liner/O- rings
• Split vent line connection to the inlet body
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Checking for Leaks
• Flow block fittings on the flow manifold
Alternately, use an electronic leak detector to check these
fittings/connections.
If these checks do not resolve the problem, contact
Agilent for service.
Low Sensitivity or Poor Repeatability
A small leak in the Multimode EPC inlet can cause low
sensitivity or poor repeatability. Check for and isolate a
small leak as described below.
If you have recently performed maintenance, first check for
leaks on any fittings/parts you handled.
1 Perform the inlet pressure decay test. If the test passes,
consider the inlet leak- free and check other possible
causes for the low sensitivity or poor repeatability.
2 If the pressure decay test fails, set the inlet to split mode.
Set a column flow of 3 mL/min, a septum purge flow of 3
mL/min, and a purge flow of 50 mL/min. Press [Prep Run].
Monitor the inlet total flow. If the total flow is much
greater than 6 mL/min, check/tighten the following
fittings:
• Septum nut
• Column
• Split vent trap
• Liner/O- ring
• Split vent line connection to the inlet body
• Flow block fittings on the flow manifold
If the problem continues, the leak may be small.
3 Use an electronic leak detector to check the
fittings/connections.
If these checks do not resolve the problem, contact
Agilent for service.
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Checking for Leaks
To Perform a MMI Pressure Decay Test
Use the Agilent Instrument Utilities Multimode Inlet Pressure
Decay Test to determine if the inlet is leaking. Open the
software, select the GC, and run the test for the inlet. See
To Perform a MMI Pressure Decay Test in the Advanced
User Guide for information on running the test.
If the test fails:
• Check the plugged column fitting and septum purge cap.
• Check the septum head. Tighten if needed.
• Replace the septum if necessary.
• Inspect and re- install the liner if it is leaking.
• Tighten the split vent trap if needed, or install a new
cartridge and O- rings.
• Tighten the split vent line connection to the inlet.
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Checking for Leaks
To Perform a PP Pressure Decay Leak Test
Use the Agilent Instrument Utilities Purged/Packed Inlet
Pressure Decay Test to determine if the inlet is leaking.
Open the software, select the GC, and run the test for the
inlet.
If the Instrument Utilities software is not available, refer to
the procedure described in the Advanced User Guide.
If the test fails:
• Tighten the septum nut/Merlin cap.
• Replace the septum or Merlin Microseal.
• Tighten the top insert weldment. Replace the liner.
• Replace the O- ring and tighten the column adapter
connection. Re- install if needed.
• Check the plugged column fitting and the septum purge
cap.
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Checking for Leaks
To Perform a COC Pressure Decay Leak Test
Use the Agilent Instrument Utilities Cool On- Column Inlet
Pressure Decay Test to determine if the inlet is leaking.
Open the software, select the GC, and run the test for the
inlet.
If the Instrument Utilities software is not available, refer to
the procedure described in the Advanced User Guide.
If the test fails:
• Check the plugged column fitting and the septum purge
cap.
• Tighten the septum nut.
• Replace the septum if necessary.
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Checking for Leaks
To Perform a PTV Pressure Decay Test
See To Perform a PTV Pressure Decay Test in the Advanced
User Guide for information on running the test.
If the test fails:
• Check the plugged column fitting and septum purge cap.
• Check the septum head. Tighten if needed.
• Replace the septum if necessary.
• If using a septumless head, tighten. Rebuild as needed.
• Inspect and re- install the liner if it is leaking.
• Replace the inlet adapter if it is leaking.
• Tighten the split vent trap if needed, or install a new
cartridge and O- rings.
• Tighten the split vent line connection to the inlet.
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Checking for Leaks
To Perform a VI Pressure Decay Test
See To Perform a VI Pressure Decay Test in the Advanced
User Guide for information on running the test.
If the test fails:
• Check the plugged column fitting and septum purge cap.
• Tighten the pneumatic connections to the volatiles
interface. Install new seals as needed.
• Tighten the split vent trap if needed, or install a new
cartridge and O- rings.
Agilent 7890A Troubleshooting
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Checking for Leaks
Agilent 7890A Troubleshooting
Agilent 7890A Gas Chromatograph
Troubleshooting
8
Troubleshooting Tasks
To Measure a Column Flow 140
To Measure a Split Vent or Septum Purge Flow 144
To Measure a Detector Flow 146
To Perform the GC Self-Test 151
To Check or Monitor Split Vent Line Backpressure 152
To Run the Inlet Trap Check 155
To Perform a SS Split Vent Restriction Test 157
To Adjust the FID Lit Offset 158
To Verify That the FID Flame Is Lit 159
To Verify FID Ignitor Function During Ignition Sequence 160
To Measure FID Leakage Current 161
To Measure FID Baseline Output 162
To Isolate the Cause of FID Noise 163
To Measure NPD Leakage Current 164
To Check for a Plugged FID Jet 165
To Check for a Plugged NPD Jet 166
To Verify That the NPD Bead Is Ignited 167
To Verify That the FPD Flame Is Lit 168
To Adjust the FPD Lit Offset 169
When to Change Gas Purifiers 170
To Check a Split Vent Line for Contamination 171
To Ignore a Device’s Readiness State 173
Agilent Technologies
139
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Troubleshooting Tasks
To Measure a Column Flow
Measuring FID, TCD, uECD, and FPD column flow
The following procedure can be used to measure column
flow with an FID, TCD, uECD, and FPD.
WA R N I N G
Hydrogen (H2) is flammable and is an explosion hazard when
mixed with air in an enclosed space (for example, a flow meter).
Purge flowmeters with inert gas as needed. Always measure
gases individually. Always turn off detectors to prevent
flame/bead autoignition.
WA R N I N G
Be careful! The detector may be hot enough to cause burns. If the
detector is hot, wear heat-resistant gloves to protect your hands.
1 Gather the following:
• Appropriate flowmeter adapter tube (can be found in
the GC ship kit)
• Electronic flowmeter calibrated for the gas and flow
rates of concern
2 Turn off the detector.
3 Turn off the detector flows.
4 Connect the appropriate adapter to the detector exhaust.
NOTE
Flowmeter tube diameters vary by model; modify the adapter to the
flowmeter tubing as needed.
A 1/8- in rubber adapter tube attaches directly to a uECD
or TCD exhaust vent.
A separate adapter (19301- 60660) is supplied for the FID.
Insert the adapter into the detector exhaust vent as far as
possible. You will feel resistance as the adapter O- ring is
forced into the detector exhaust vent. Twist and push the
adapter during insertion to ensure a good seal.
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Troubleshooting Tasks
For the FPD, remove the plastic tubing from the FPD
exhaust and connect the flowmeter directly to the FPD
vent tube. If necessary, use a 1/4- inch tube adapter
between the detector exhaust and the flowmeter tubing.
5 Connect the flowmeter to the flowmeter adapter to
measure flow rates.
Agilent 7890A Troubleshooting
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Troubleshooting Tasks
Measuring NPD column flow
1 Gather the following:
• NPD flowmeter adapter tool (G1534- 60640)
• Flow- measuring insert (19301- 60660)
• Electronic flowmeter calibrated for the gas and flow
rates of concern
2 Set the bead voltage to 0.0 V.
3 Cool the NPD to 100 °C.
WA R N I N G
Be careful! The detector may be hot enough to cause burns. If the
detector is hot, wear heat-resistant gloves to protect your hands.
4 Remove the bead and store it carefully until reinstallation.
5 Insert the NPD flowmeter adapter tool into the NPD
collector.
6 Attach the flow- measuring insert to the NPD flowmeter
adapter tool.
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Troubleshooting Tasks
8
7 Place the flowmeter tubing over the flow- measuring insert
to begin measuring flows.
Agilent 7890A Troubleshooting
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Troubleshooting Tasks
To Measure a Split Vent or Septum Purge Flow
Note that the GC reports flows calibrated to 25 °C and
1 atmosphere. Correct flowmeter results accordingly.
WA R N I N G
Hydrogen (H2) is flammable and is an explosion hazard when
mixed with air in an enclosed space (for example, a flow meter).
Purge flowmeters with inert gas as needed. Always measure
gases individually. Always turn off detectors to prevent
flame/bead autoignition.
Septum purge and split vent flows exit through the
pneumatic module at the top rear of the GC. See the figure
below.
Back inlet split
vent
Back inlet purge
vent
Front inlet split
vent
Front inlet
purge vent
To measure split vent or septum purge flows, attach the
flowmeter to the appropriate tube. Remove the GC
pneumatics cover to access the back inlet exhausts.
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Agilent 7890A Troubleshooting
Troubleshooting Tasks
8
• The split vent has a 1/8- in Swagelok threaded fitting.
Create and use a 1/8- in tube adapter (as shown below) to
convert the 1/8- in threaded fitting into a 1/8- in tube.
This prevents the rubber flowmeter tubing from leaking
around the threads, which will result in leakage and thus
an incorrect flow reading.
• The septum purge is a 1/8- in tube. Use the red rubber
adapter shown to measure flows.
Agilent 7890A Troubleshooting
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Troubleshooting Tasks
To Measure a Detector Flow
Detectors, especially detectors with flame, require precise
flow measurements to function properly. Incorrect flows are
caused by:
• Restrictions in the supply line, which will cause a Not
Ready message on the GC display (all detectors)
• A leaking column or column adapter fitting (all detectors)
• A plugged jet (FID, NPD).
• A leak in the burner chamber, window seal, or ignitor
seal (FPD)
• A pressure sensor that needs to be zeroed. (See To Zero
the EPC Module Pressure Sensor.)
• An EPC valve that is not operating correctly.
To isolate the problem, compare the flow of one channel of
gas against the actual flow rate.
Measuring FID, TCD, uECD, and FPD flows
WA R N I N G
Hydrogen (H2) is flammable and is an explosion hazard when
mixed with air in an enclosed space (for example, a flow meter).
Purge flowmeters with inert gas as needed. Always measure
gases individually. Always turn off detectors to prevent
flame/bead autoignition.
1 Gather the following:
• Appropriate flowmeter adapter tube (can be found in
the GC ship kit)
• Electronic flowmeter calibrated for the gas and flow
rates of concern
CAUTION
To avoid damaging the column, cool the oven before turning off the
column flow.
2 Set the oven temperature to ambient (35 °C).
3 Turn off the column flow and pressure.
4 Shut off all detector gases.
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Troubleshooting Tasks
5 Turn off (where applicable): the FID flame, FPD flame,
and TCD filament.
6 Cool the detector.
7 Connect the appropriate adapter to the detector exhaust.
NOTE
Flowmeter tube diameters vary by model; modify the adapter to the
flowmeter tubing as needed.
A rubber adapter tube attaches directly to a uECD, or
TCD exhaust vent.
A separate adapter (19301- 60660) is supplied for the FID.
Insert the adapter into the detector exhaust vent as far as
possible. You will feel resistance as the adapter O- ring is
forced into the detector exhaust vent. Twist and push the
adapter during insertion to ensure a good seal.
For the FPD, remove the plastic tubing from the FPD
exhaust and connect the flowmeter directly to the FPD
vent tube. If necessary, use a 1/4- inch tube adapter
between the detector exhaust and the flowmeter tubing.
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Troubleshooting Tasks
8 Connect the flowmeter to the flowmeter adapter.
9 Measure the actual flow rate of each gas one at a time.
Measuring NPD flows
1 Gather the following:
• NPD flowmeter adapter tool (G1534- 60640)
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Troubleshooting Tasks
• Flow- measuring insert (19301- 60660)
• Electronic flowmeter calibrated for the gas and flow
rates of concern
2 Set the bead voltage to 0.0 V.
3 Cool the NPD to 100 °C.
WA R N I N G
Be careful! The detector may be hot enough to cause burns. If the
detector is hot, wear heat-resistant gloves to protect your hands.
4 Remove the bead and store it carefully until reinstallation.
5 Insert the NPD flowmeter adapter tool into the NPD
collector.
6 Attach the flow- measuring insert to the NPD flowmeter
adapter tool.
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Troubleshooting Tasks
7 Place the flowmeter tubing over the flow- measuring insert
to begin measuring flows.
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Agilent 7890A Troubleshooting
Troubleshooting Tasks
8
To Perform the GC Self-Test
1 Turn the GC off.
2 Wait 1 min, then turn the GC back on. If the main GC
status screen appears, the GC has passed the self- test.
Agilent 7890A Troubleshooting
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Troubleshooting Tasks
To Check or Monitor Split Vent Line Backpressure
Agilent provides a built- in test that measures backpressure
in the split vent trap and line for the split/splitless,
multimode, PTV, and VI inlets. The test measures the
pressure developed in the split vent flow path at a given,
user- selected flow rate. This flow rate can be your method
Split flow setpoint, or the default 400 mL/min used by Agilent
to compare “typical” values.
By running the test on a clean system, you can establish a
baseline for expected backpressure in the split vent line.
Then, you can re- run the test periodically to determine
whether or not the trap needs to be replaced before it
impacts your chromatography.
The pressure measured by the test depends on:
• The liner installed
• The flow rate used
Therefore, the actual measured value will vary between
different setups and from GC to GC.
The test checks for:
• Liner restriction
• Contamination on the gold seal (split/splitless inlet only)
• Restrictions in the split vent line, such as condensed
sample contamination in the split vent line and trap
The test can also provide a measure of suitability for the
installed hardware. Run the test using your method’s
setpoints and hardware. If the measured test pressure is
close to the desired column head pressure, this means that
even a minor amount of restriction in the split vent line can
cause the GC to become not ready. You may wish to install
a different liner or adjust the method. (For splitless liners,
first try reinstalling the liner. Splitless liners create more
backpressure than split liners, and so minor variations in
orientation can make a difference at low head pressures.)
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To set a warning limit for the inlet trap check
To use the inlet trap check to monitor the split vent trap:
1 If the existing split vent trap has been used for many
sample injections, replace it. Make sure that the GC is
clean:
• Replace inlet hardware if needed.
• Check that the split vent line is free from
contamination or restrictions.
2 Run the inlet trap check. See “To Run the Inlet Trap
Check”.
3 Note the pressure. This reading is the backpressure you
can expect from a clean system with the installed liner.
4 Determine a practical split vent backpressure limit.
Use the GC normally. Periodically rerun the inlet trap
check. You will need to change the split vent trap when
either:
• You see chromatographic issues related to a restriction
in the split vent, typically poor split mode area
repeatability, or
• The reported test pressure approaches or exceeds the
method column head pressure setpoint.
Run the inlet trap check and note the pressure. Change
the split vent trap.
5 Set a warning limit and behavior, if desired.
Now that you know when the trap needs to be changed,
you can set one or two limits in the test. Use these limits
to set the service due indicator, or to force the GC to go
Not ready. The two limits are:
• Warning if pressure check: If the measured pressure
exceeds the limit, turn on the service due indicator.
• Fault if pressure check: If the measured pressure exceeds
the limit, make the GC Not Ready.
To set a warning limit:
a Press [Service Mode], scroll to Front inlet trap check or to
Back inlet trap check, then press [Enter].
b Scroll to the desired limit.
c Enter a limit using the keypad, then press [Enter].
(To disable a warning, select it then press [Off/No].)
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The test is now set up.
6 Periodically rerun the test. When the test fails, replace
the split vent trap.
To clear a Not Ready condition or to turn off the Service
Due indicator:
1 Press [Service Mode], scroll to Front inlet trap check or to
Back inlet trap check, then press [Enter].
2 Scroll to Reset the test results? and press [On/Yes].
To disable a warning limit for the inlet trap check
1 Press [Service Mode], scroll to Front inlet trap check or Back
inlet trap check, then press [Enter].
2 Scroll to the warning, then press [Off/No].
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To Run the Inlet Trap Check
From the GC keypad:
1 Press [Service Mode], scroll to Front inlet trap check or Back
inlet trap check, then press [Enter]. The display will be
similar to Figure 5:
FRONT INLET TRAP CHECK
Inlet Pressure
5.471 psi<
Test Inlet
(ON to Start)
Test flow rate
400mL/min
Warning if pressure check OFF
Fault if pressure check
OFF
Last test results
Tue Oct 20 16:07 2009
Test pressure OK:
4.8
Reset the test results? (yes)
Figure 5
Example front inlet trap check display. Example assumes a test
has been previously run. Scroll to see all lines of the display.
2 Scroll to Test flow rate and enter a flow rate. A typical flow
rate for this test is 400 mL/min, but you may find other
values more appropriate for your setup.
3 Scroll to Test Inlet and press [On/Yes] to start the test.
4 Wait while the pressure stabilizes. When stable, the Test
Inlet line of the display changes to Test pressure OK x.xx,
where x.xx is the current pressure.
If the inlet cannot achieve the test setpoint, check for a
leak (at the inlet, split vent trap, or split vent line) or low
supply gas pressure.
5 Note the resulting Inlet Pressure. If the measured pressure
exceeds any limits you have set up, the GC will respond
accordingly. See “To Check or Monitor Split Vent Line
Backpressure”.
Typical pressures for a clean split flow path are:
• 1–2 psi (7–14 kPa) at 400 mL/min for a split liner
• 3–10 psi (21–69 kPa) at 400 mL/min for a splitless
liner
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If the pressure for a splitless liner seems abnormally high
for a clean system, try reinstalling the liner.
If pressure on a clean system is within these ranges, but
is near the operating pressure for the method, consider a
change in hardware or the method. See also Cannot
Maintain a Pressure as Low as the Setpoint on a Split
Inlet.
6 Press [Off/No] to stop the test.
NOTE
The most recent test results display at the bottom of the display. Scroll
down to see them.
To clear a Not Ready condition or Service Due indicator,
scroll to Reset the test results? and press [On/Yes].
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To Perform a SS Split Vent Restriction Test
Use the Agilent Instrument Utilities Split Vent Restriction
Test to determine if there is an abnormal restriction in the
split vent flow path. Open the software, select the GC, and
run the test for the inlet. (Alternately, see “To Run the Inlet
Trap Check”.)
If the test fails:
• Consider whether the setup exceeds the minimum viable
pressures obtainable by the GC. See also Table 4.
• Consider the liner used. Agilent recommends a low
pressure- drop liner for split analyses, part number
5183- 4647.
• Replace the split vent trap filter.
• Inspect and replace the gold seal. If not using the low
pressure drop liner, consider installing a high- flow gold
seal, 5182- 9652.
• Check for contamination in the split vent line. See “To
Check a Split Vent Line for Contamination”.
If the problem remains, contact Agilent for service.
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To Adjust the FID Lit Offset
To adjust the FID Lit offset:
1 Press [Config].
2 Scroll to Front detector or Back detector (wherever the
detector is installed) and press [Enter].
3 Scroll to Lit offset. With the Lit offset line highlighted, enter
the new parameter for the detector and press [Enter].
4 Lit offset should be < 2.0 pA or lower than the normal
FID output when lit.
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To Verify That the FID Flame Is Lit
To verify that the FID flame is lit, hold a mirror or other
reflective surface over the collector exhaust. Steady
condensation indicates that the flame is lit.
Typically the FID output will be between 5.0 and 20.0 pA
when lit and < 2.0 pA when not lit.
If the flame does not light, do the following:
• Verify that the detector temperature is above 150 °C.
Agilent recommends operating the FID ≥300 °C.
• Verify correct detector flows.
• Inspect the jet for contamination.
• Verify that the jet is installed correctly.
• Check the column connections for leaks.
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To Verify FID Ignitor Function During Ignition Sequence
WA R N I N G
Keep body parts at a safe distance from the FID chimney while
performing this task. If using hydrogen, the FID flame will not be
visible.
1 Remove the detector top cover.
2 Turn the FID flame On.
3 Observe the ignitor plug though the FID chimney. The
small hole should glow during ignition sequence.
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To Measure FID Leakage Current
1 Load the analytical method.
• Make sure flows are acceptable for ignition.
• Heat the detector to operating temperature or to
300 °C.
2 Turn off the FID flame.
3 Press [Front Det] or [Back Det], then scroll to Output.
4 Verify that the output is stable and < 1.0 pA.
If the output is unstable or > 1.0 pA, turn off the GC and
check for proper assembly of the upper FID parts and for
contamination. If the contamination is confined to the
detector, bakeout the FID.
5 Turn on the flame.
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To Measure FID Baseline Output
1 With the column installed, load your checkout method.
2 Set the oven temperature to 35 °C.
3 Press [Front Det] or [Back Det], then scroll to Output.
4 When the flame is lit and the GC is ready, verify that the
output is stable and < 20 pA (this may take some time).
5 If the output is not stable or > 20 pA, the system or gas
may be contaminated. If this contamination is isolated to
the detector, bakeout the FID.
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To Isolate the Cause of FID Noise
FID noise is the result of mechanical, electrical and chemical
factors. FID noise can be a subjective parameter. Often FID
baseline noise is perceived based on history of a given
detector or comparison with another detector in the lab. For
proper diagnosis of noise it is important to evaluate the
detector noise under documented conditions against a known
standard. Find more detailed information about noise in
Noisy Detector, Including Wander, Drift, and Baseline Spikes.
Before troubleshooting the detector, perform a noise test
using your Agilent data system. If the detector fails the
noise test, then troubleshoot the cause as described below.
To isolate the cause of FID noise:
1 If the noise test fails, remove the column and re- evaluate
detector noise with the FID capped and re- ignited, using
only H2/air and makeup detector gases. If it passes,
suspect contaminated column/carrier gas.
2 If the noise failed with no column installed, repeat the
noise test with only H2 and air - set makeup flow to
"Off". If it passes, suspect contaminated makeup gas.
3 If the noise test still fails, see To Measure FID Leakage
Current. If the leakage test fails, replace or clean the
collector and Teflon insulators, the interconnect with
spring, and/or the entire FID electrometer assembly. If the
leakage test fails, replace or clean the collector and Teflon
insulators, the interconnect with spring, and/or the entire
FID electrometer assembly.
4 If the leakage current test is OK, suspect a contaminated
jet or contaminated H2 or Air detector gas supplies
(gases, tubing, traps), especially if the background of the
detector when lit is >20 pA.
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To Measure NPD Leakage Current
1 Load the analytical method.
2 Set the NPD Adjust Offset to Off and the Bead Voltage to
0.00 V.
• Leave the NPD at operating temperature.
• Leave flows on or off.
3 Press [Front Det] or [Back Det], then scroll to Output.
4 Verify that the output (leakage current) is stable and
< 1.0 pA.
5 The output should slowly drop toward 0.0 pA, and should
stabilize in the tenths of a picoamp. Current > 2.0pA
indicates a problem.
If the current is > 2.0pA, do the following:
• Inspect the jet for contamination.
• Check the column or column adapter fitting for leaks.
• Ensure that the metal sealing ring is not crushed or
misaligned. See To Maintain the NPD Collector, Ceramic
Insulators, and Jet
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To Check for a Plugged FID Jet
The most common cause of FID ignition problems is a
plugged or partially plugged jet. If the jet is not completely
plugged and the flame still ignites, a secondary symptom
will be lengthening peak retention times. Jet plugging is
most common with thick- film/high bleed or packed columns
and high temperature applications. It is best to operate the
column oven within the temperature limits of the column
and also to operate the FID at least 20 °C hotter than the
maximum oven temperature in the GC method. If the FID jet
is becoming plugged, actual H2, Makeup and Capillary
carrier flows will be lower than the values indicated by the
GC.
To check for a plugged FID jet:
1 Leave the column installed in the FID. If already removed,
cap off the detector column fitting in the oven. (Leaving
the column installed will determine if the column is
installed too high in the jet, plugging the orifice.)
2 Set the makeup flow to “Off”. Confirm a reading on the
GC display of 0.0 mL/min for actual makeup flow. If not
0.0 – follow the procedure To Zero the EPC Module
Pressure Sensor.
3 Set the hydrogen flow to 75 mL/minute (increase the H2
supply pressure as needed to achieve this flow rate
setting.)
4 Monitor the makeup flow “Actual” reading
If the makeup flow is indicating a value in excess of
1.0 mL/min, this indicates that the jet is plugged or
partially plugged; pressure is backing up from the H2
channel into the makeup channel of the EPC system,
resulting in a false flow indication on the makeup
channel.
Alternately, remove the jet from the housing and hold it up
to a light source. Check the holes in the jet for
contamination. If plugged, replace the jet.
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To Check for a Plugged NPD Jet
The detector EPC module controls flow by maintaining a
calibrated gas pressure against a fixed restriction. A plugged
jet will cause inaccurate flow readings.
To check for a plugged NPD jet, measure the actual hydrogen
and makeup flows. (See Measuring NPD flows.) If the flows
are lower than the displayed values, replace the jet.
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To Verify That the NPD Bead Is Ignited
WA R N I N G
Hot exhaust! Detector exhaust is hot and can cause burns.
To verify that the bead is ignited, look through the vent hole
on the detector lid to see if the bead is glowing orange.
The NPD output is selected by the operator as part of the
adjust offset process and generally is between 5.0 and
50.0 pA.
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To Verify That the FPD Flame Is Lit
To verify that the FPD flame is lit:
1 Remove the rubber drip tube from the detector vent.
2 Hold a mirror or shiny surface near the aluminum
exhaust tube. Steady condensation means that the flame
is lit.
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To Adjust the FPD Lit Offset
To adjust the FPD Lit offset:
1 Press [Config].
2 Scroll to Front detector or Back detector (wherever the
detector is installed) and press [Enter].
3 Scroll to Lit offset. With the Lit offset line highlighted, enter
the new parameter for the FPD (typical value is 2.0 pA),
and press [Enter].
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When to Change Gas Purifiers
Agilent highly recommends using purifying traps in the gas
lines to prevent impurities from entering and contaminating
the GC system or damaging the column. Some traps are
single- purpose for the removal of oxygen, moisture, or
hydrocarbons, while combination traps remove all those
contaminants.
The best way to know when it is time to change a trap is to
use an indicating trap, which should be placed after a high
capacity trap. Agilent recommends using glass indicating
traps, whose clear tubes display a distinct color change in
response to a specific contaminant. This color change tells
the analyst it is time to change traps.
If no indicating traps are used, it is best to follow the
manufacturer’s recommendation for replacement frequency.
Typically, the manufacturer will state how many gas
cylinders can be purified with a given trap. If desired, it is
possible to estimate when to replace the trap by performing
a rough calculation. For example: you have a standard “K”
size cylinder with He at 99.995% purity that contains 7,800 L
of He. Assuming a worst case scenario in which the
remaining 0.005% is all oxygen, you should have 39 mL, or
about 56 mg of O2 in the tank. Agilent’s OT3 oxygen trap,
for example, has a capacity of 600 mg O2. Therefore, you
need to replace the OT3 trap every 10 cylinders. This is just
a rough estimate, and it is prudent to change traps too early
rather than too late.
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To Check a Split Vent Line for Contamination
This procedure applies to the multimode and split/splitless
inlets.
WA R N I N G
Be careful! The oven, inlet, and/or detector may be hot enough to
cause burns. If the oven, inlet, or detector is hot, wear
heat-resistant gloves to protect your hands.
1 Gather the following:
• 7/16- inch wrench
• Wrench, hex for changing septum
• Heat- resistant gloves if the inlet is hot
• Cleaning brushes
2 Load the inlet maintenance method and wait for the GC
to become ready.
3 Loosen the 1/8- inch Swagelok nut that seals the copper
split vent line to the injection port.
4 Inspect the 1/8- inch copper split line for condensed
sample. Flush or replace the copper split vent line.
5 Remove the septum head.
6 Check the split tube fitting in the shell weldment for
blockage. Clean the split tube with a brush and suitable
solvent.
7 Reassemble the split/splitless inlet and run the split vent
restriction test to test for restrictions in the split vent
flow path. If the inlet still fails, suspect flow module
contamination or defects.
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8 Check for leaks. Run the pressure decay test. See “To
Perform a SS Pressure Decay Leak Test” or “To Perform a
MMI Pressure Decay Leak Test”.
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To Ignore a Device’s Readiness State
By default, the GC monitors the status of all configured
devices (inlets, detectors, valve box heaters, valves, oven
heater, EPC modules, and so forth) and becomes ready when
all of them reach setpoint. If the GC senses a problem in
one of these devices, the GC will either never become ready,
or may go into a shutdown state to protect itself or prevent
a safety hazard. However, there may be a time when you do
not wish to have the readiness state of a device prevent a
run from starting. An important example is when an inlet or
detector heater is defective. Normally, this fault prevents the
GC from becoming ready and starting a run. However, you
can set the GC to ignore this problem so that you can use
the other inlet or detector until the device is repaired.
Not all devices can be ignored. You can ignore the readiness
state of inlets, detectors, the oven, or an EPC module. The
readiness state of other devices and components can never
be ignored, for example, injection devices such as a
switching valve or automatic liquid sampler.
To ignore the status of a device:
1 Turn off the device’s heater and gas flows as applicable.
(Make sure that it cannot create a safety hazard.)
2 Press [Config], then select the element.
3 Scroll to Ignore Ready and press [On/Yes] to set it to True.
You can now use the GC until the device is repaired.
CAUTION
Do not ignore the readiness state of a device that is being used
unless you do not care if it reaches setpoint.
Be sure to return a broken device to Ignore Ready = False after it is
repaired. Otherwise, its state (temperature, flow, pressure, and so
forth) will continue to be ignored, even if using this device in the
analysis.
To consider a device’s readiness, set Ignore Ready to False.
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