Agilent 490 Micro Gas Chromatograph

User Manual

4

GC Channels

Carrier Gas 46

Micro Electronic Gas Control (EGC) 47

Injector 47

Column 48

Backflush Option 57

TCD Detector 60

The instrument contains up to 2 channels in a dual channel cabinet, or up to 4 channels for a quad channel cabinet. A GC channel contains a gas regulator, an injector, a column, and a

TCD detector. See Figure 18 on page 46.

This chapter provides a brief discussion on the major components in the Micro GC and the backflush option.

Agilent Technologies

45

4

GC Channels

Carrier Gas

C A U T I O N

The Micro GC is configured for use with either He and H

2 or



N

2

and Ar.

Agilent recommends you use gases with a minimum purity of

99.995%. Since the injection valve is operated pneumatically, there is a limit of 550 kPa ± 10% (80 psi ± 10%) to the main gas supply.

Your Micro GC is configured either for carrier gas He and H

2 or N

2

and Ar.

Use the carrier gas type for which your instrument is configured, otherwise the detector filaments can be damaged.

Gas Clean unit

(optional)

Microelectronic gas control

(EGC)

Injector

Columns

(analytical and reference)

µTCD

Reference vent

Column vent

Sample Out

Carrier gas

Figure 18 Gas flow diagram

Sample in

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4

Micro Electronic Gas Control (EGC)

The Micro GCs have built-in regulators that can be adjusted to get a constant or programmed pressure control, which, once constant or programmed pressure control is obtained, results in a constant or programmed flow through the injector, column and detector. The pressure range is from 50 to 350 kPa (7 to

49 psi). This pressure sets a continuous flow of carrier gas of about 0.2 to 4.0 mL/min (depending on column length and type).

A typical pressure rise is 200 kPa/min, which will give a significant pressure increase during the run without excessive baseline disturbance. In most cases baseline subtraction may improve the quality of chromatograms that suffer from baseline drift.

Injector

The injector has a built-in 10-µL sample loop that is filled with the gaseous sample. The pressure of the sample should be between 0 and 100 kPa (0 to 15 psi) and the sample temperature within 5 to 110 °C ± 5 °C of the analyzer.

When the chromatographic data system sends a START command, the vacuum pump draws the gas sample through the loop and the injector injects the gas sample from the sample loop into the gas stream. A typical injection time is 40 milliseconds (ms). This equals an average injection volume of

200 nL. Injection time will be rounded to a multiple of 5 ms. A practical minimum value is 40 ms. A value of 0 to 20 milliseconds might result in no injection.

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GC Channels

Column

A variety of column configurations are possible on the Micro

GC. The columns you require for your specific analyses have been installed at the factory. Other configurations are, of course, possible, but altering the GC channels is a delicate matter that can only be handled by an Agilent service engineer.

Table 7

shows several standard columns as supplied in the

Micro GCs and selected applications. Other columns are available by contacting Agilent Technologies.

Table 7

Agilent Micro GC columns and applications

Column/Phase type

Molsieve 5Å

Hayesep A

CP-Sil 5 CB

CP-Sil 19 CB

CP-WAX 52 CB

PLOT Al

2

O

3

/KCl

PoraPLOT U

PoraPLOT Q

CP-CO

X

CP-Sil 19CB for THT

CP-Sil 13CB for TBM

MES NGA

Target components

Permanent gases (N

2

/O

2

separation), methane, CO, NO, and so forth. 20 m required for O

2

-Ar baseline separation). Natural gas and biogas analysis. Optional Retention

Time Stability (RTS) configuration.

Hydrocarbons C

1

–C

3

, N

2

, CO

2

, air, volatile solvents, natural gas analysis.

Hydrocarbons C

3

–C

10

, aromatics, organic solvents, natural gas analysis.

Hydrocarbons C

4

–C

10

, high boiling solvents, BTX.

Polar volatile solvents, BTX.

Light hydrocarbons C

1

–C

5

saturated and unsaturated. Refinery gas analysis.

Hydrocarbons C

1

–C

6

, halocarbons/freons, anesthetics, H

2

S, CO solvents. Separation of ethane, ethylene, and acetylene.

2

, SO

2

, volatile

Hydrocarbons C

1

–C

6

, halocarbons/freons, anesthetics, H

2

S, CO

2

, SO

2

, volatile solvents. Separation of propylene and propane, coelution of ethylene and acetylene.

and O

2

), CH

4

.

THT and C

3

–C

6

+

in Natural Gas Matrix.

TBM and C

3

–C

6

+

in Natural Gas Matrix.

Unique column specially tested for MES in natural gas (1 ppm)..

C A U T I O N

All columns except the HayeSep A (160 °C) and MES (110 °C) columns can be used up to 180 °C, the maximum temperature of the column oven.

Exceeding this temperature will cause the column to lose efficiency instantly and the column module will need replacement. All channels have a built-in protection that prevents a setpoint above the maximum temperature.

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Molsieve 5Å columns

The Molsieve 5Å column is designed to separate: hydrogen, carbon monoxide, methane, nitrogen, oxygen, and some noble gases. Higher molecular weight components have much higher retention times on this column.

Table 8

Molsieve 5Å instrument parameters

Parameter

Column temperature

Injector temperature

Column pressure

Sample time

Injection time

Run time

Detector sensitivity

Peak 1

Peak 2

Peak 3

Peak 4

Peak 5

4m Heated

110°C

110°C

100 kPa (15 psi)

30 s

40 ms

25 s

Auto

Hydrogen 1.0%

Argon/Oxygen 0.4%

Nitrogen 0.2%

_________

_________

10m Unheated

40°C

NA

150 kPa (21 psi)

30 s

40 ms

140 s

Auto

Neon 18 ppm

Hydrogen 1.0%

Argon 0.2%

Oxygen 0.2%

Nitrogen 0.2%

20m Unheated

40 °C

NA

200 kPa (28 psi)

30 s

40 ms

210 s

Auto

Neon 18 ppm

Hydrogen 1.0%

Argon 0.2%

Oxygen 0.2%

Nitrogen 0.2%

6

4

2

0 mV

14

Molsieve 5Å 4 m heated

2

12

10

8

3

1

0 5 10 15 20 25

Seconds mV

4.5

4

3.5

Molsieve 5Å 10 m unheated

3

4

mV

450

400

350

3

2.5

2

1.5

5

1

0.5

12

0

0 20 40 60 80 100 120 140 160 seconds

300

250

200

150

100

50

0

0

Molsieve 5Å 20 m unheated

1

50

2

3

4

100 150

5

200 250

Seconds

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GC Channels

CP-Sil 5 CB columns

The natural gas components, mostly hydrocarbons, separate in the same order on the non-polar and medium-polar CP-Sil CB columns. Nitrogen, methane, carbon dioxide, and ethane are not separated on these columns. They produce a composite peak.

For separation of these components, consider a HayeSep A column.

Table 9

CP-Sil 5 CB instrument parameters

Parameters

Column temperature

Injector temperature

Column pressure

Sample time

Injection time

Run time

Detector sensitivity

Peak 1

Peak 2

Peak 3

Peak 4

Peak 5

4m Heated

50 °C

110 °C

150 kPa (21 psi)

30 s

40 ms

30 s

Auto

Composite Balance

Ethane 8.1%

Propane 1.0% i-Butane 0.14% n-Butane 0.2%

6m Unheated

50 °C

NA

150 kPa (21 psi)

30 s

40 ms

30 s

Auto

Composite Balance

Ethane 8.1%

Propane 1.0% i-Butane 0.14% n-Butane 0.2%

25

15

5

-5

0 mV

55

CP Sil 5 CB 4 m heated

1 2

45

3

35

5

4 5

10 15 20 25 30 35

Seconds

24

19

14

9 mV

34

CP Sil 5 CB 6 m unheated

1 2 3

29

4

5

4

-1

0 10 20 30 40 50 60 70

Se conds

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CP-Sil CB columns

Table 10

CP-Sil CB instrument parameters

Parameter

Column temperature

Injector temperature

Column pressure

Sample time

Injection time

Run time

Detector sensitivity

Peak 1

Peak 2

Peak 3

CP-Sil 13 CB 12m Heated (TBM) CP-Sil 19 CB 6m Heated (THT)

40°C 85 °C

50°C

250 kPa (38 psi)

85 °C

200 kPa (25 psi)

30 s

255 ms

80 s

Auto

30 s

255 ms

35 s

Auto

Methane balance

TBM 6.5 ppm

________

Helium balance

THT 4.6 ppm

Noane 4.5 ppm mV

0.6

0.4

0.2

0

-0.2

-0.4

-0.6

-0.8

0

CP Sil 13 CB

12 m heated (TBM)

10 20

1

30 40 50

2

60 70 80 90

Se conds

-0.5

-1

-1.5

mV

0.5

CP Sil 19 CB

6 m unheated (THT)

1

0

-2

0 10 20 30

2

3

40 50 60

Seconds

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GC Channels

PoraPlot 10m column

Table 11

PoraPlot 10m instrument parameters

Parameter

Column temperature

Injector temperature

Column pressure

Sample time

Injection time

Run time

Detector sensitivity

Peak 1

Peak 2

Peak 3

Peak 4

Peak 5

4

5

2

3

Auto

1

PoraPlot u 10m Heated PoraPlot Q 10m Heated

150°C

110°C

150 °C

110 °C

150 kPa (21 psi)

30 s

40 ms

100s

150 kPa (21 psi)

30 s

40 ms

50 s

Auto

Composite Balance

Ethane 8.1%

Propane 1.0% i-Butane 0.14% n-Butane 0.2% mV PoraPlot U 10 m heated

30

25

20

15

50

45

40

35

10

5

0

2 6

1 2

3

4

5

10 14 18 22 26 30 34 38 42 46 50

Seconds mV

680

580

480

380

280

180

80

-20

0

PoraPlot Q 10 m heated

10 20

1 2

30

3

40

4

5

50 60

Seconds

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Hayesep A 40 cm heated column

WA R N I N G

The HayeSep A column separates oxygen, methane, carbon dioxide, ethane, acetylene, ethylene, and selected sulfur gases.

Nitrogen coelutes with oxygen. Components with a higher molecular weight than propane have long retention times on this column.

Maximum allowable column temperature is 160 °C.

Table 12

Hayesep instrument parameters

Parameter

Column temperature

Injector temperature

Column pressure

Sample time

Injection time

Run time

Detector sensitivity

Peak 1

Peak 2

Peak 3

Hayesep A 40 cm Heated

50 °C

110 °C

150 kPa (21 psi)

30 s

40 ms

60 s

Auto

Nitrogen 0.77%

Methane Balance

Ethane 8.1%

245

195

145

95 mV

345

Hayesep A 40 cm heated

2

295

45

-5

0

1

10 20 30

3

40 50 60 70

Seconds

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GC Channels

CO

X

and AL

2

0

3

/KCI columns

Table 13

CO

X

and AL

2

0

3

/KCI instrument parameters

Parameter

Column temperature

Injector temperature

Column pressure

Sample time

Injection time

Run time

Detector sensitivity

Peak 1

Peak 2

Peak 3

Peak 4

Peak 5

CO

X

1m Unheated

80 °C

NA

200 kPa (28 psi)

30 s

40 ms

204 s

Auto

Hydrogen 1.0%

Nitrogen 1.0%

CO 1.0%

Methane 1.0%

CO

2

1.0%

Helium Balance

AL

2

0

3

/KCI 10m Heated

100

°C

110

°C

150 kPa (21 psi)

30 s

40 ms

60 s

Auto

Composite Balance

Ethane 8.1%

Propane 1.0% i-Butane 0.14% n-Butane 0.2%

2.5

2

1.5

1 mV

3.5

3

CO

X

2

1 m unheated

3

4

0.5

0

1

-0.5

0 50 100

5

150 mV

115

Al

2

O

3

/KCl 10 m heated

1 2

95

75

3

55

35

200

15

250

Seconds

-5

0 10 20

4 5

30 40 50 60 70

Seconds

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MES (NGA) and CP-WAX 52 CB columns

Table 14

MES (NGA) and CP-WAX 52 CB instrument parameters

Parameter

Column temperature

Injector temperature

Column pressure

Sample time

Injection time

Run time

Detector sensitivity

Peak 1

Peak 2

Peak 3

Peak 4

MES 10m Heated (NGA) CP-WAX 52 CB 4m Heated

90 °C

110 °C

60 °C

110 °C

70 kPa (10 psi)

30 s

500 ms

120 s

150 kPa (21 psi)

30 s

40 ms

35 s

Auto

Nitrogen Balance

Noane 11.2 ppm

MES 14. 2 ppm

________

Auto

Nitrogen 0.75%

Acetone 750 ppm

Methanol 0.15%

Ethanol 0.30%

Helium Balance mV

4000

3500

3000

2500

2000

1500

1000

500

0

-500

0

MES 10 m heated (NGA)

20 40 60

1

0.9

0.5

2

3

0.1

- 0.3

80 90 100 110 120 130 mV CP-WAX 52 CB 4 m heated

1

13

8

2

3

4

3

80 100 120 140

Seconds

-2

1 6 11 16 21 26 31 36

Seconds

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GC Channels

Column conditioning

Follow this procedure to make sure that any water that might be present inside the analytical column is removed before the TCD is switched on.

Also follow this procedure if the Micro GC module has been stored for a long period.

C A U T I O N

The detector filaments may be damaged by improper conditioning. Follow this procedure to avoid damaging the detector filaments.

Column conditioning procedure

1

2

3

4

Switch off the TCD filaments in the method.

Set the column temperature of the module to the maximum temperature (160 °C or 180 °C depending on the column limit). Leave the filaments off.

Download this method to the Micro GC.

Run the downloaded method to condition the column, preferably overnight.

This will assure you that all the water has been removed from the column and no damage will occur to the TCD filaments.

Nitrogen and oxygen merging in Molsieve columns

On a properly activated column, nitrogen and oxygen will be well separated. However, in time you will find that these two peaks begin to merge together. This is caused by water and carbon dioxide present in the sample or carrier gas, adsorbing to the stationary phase.

To restore the column efficiency, condition the column, Z described above, for about an hour. After reconditioning, you can test the column performance by injecting plain air. If you have a proper separation between nitrogen and oxygen again, the column separation power has been restored. If the Micro GC frequency of use is very high, you might consider routinely leaving the oven temperature at 180 °C overnight. The longer the reconditioning period, the better the column performance.

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Backflush Option

Backflush to vent is an advanced technique used to prevent later-eluting compounds from reaching the analytical column and detector. The main reason for applying this technique is to keep the analytical column clean and reduce analysis time.

The Micro GC is optionally available with GC modules that incorporate backflush capabilities.

1 2 3 4 5

6

8

Natural gas analysis, straight

Figure 19 Natural gas analysis

7

50 s

1 = Methane

2 = Ethane

3 = Propane

4 = iso-Butane

5 = Butane

6 = iso-Pentane

7 = Pentane

1 2

3

4

5

8 50 s

Natural gas analysis, with backflush at 8 seconds

A backflush system always consists of a pre-column and an analytical column. The two columns are coupled at a pressure

point, which makes it possible to invert the carrier gas flow direction through the pre-column at a preset time, called the

backflush time. See Figure 21 on page 58.

The injector, two columns, and detector are in series.

The sample is injected onto the pre-column where a pre-separation takes place; injection takes place in normal mode. See Figure 20 on page 58.

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Restriction

System pressure

Pressure regulator

Pre-column

Analytical column

Pressure point

Detector

Injector Backflush vent

Figure 20 Backflush system normal flows

When all compounds to be quantified are transferred to the analytical column, the backflush valve switches (at the backflush time). On the pre-column, the flow inverts and all compounds left on the pre-column now backflush to the vent. On the analytical column the separation continues because there the flow is not inverted. See Figure 21 .

Restriction

System pressure

Pressure regulator

Pre-column

Analytical column

Pressure point

Detector

Figure 21 Backflush flows

Injector

Backflush vent

58

The standby mode is the backflush configuration (if the instrument is equipped with the optional backflush valve).

Backflushing saves the time required to elute high boiling components that are not of interest and ensures that the pre-column will be in good condition for the next run.

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Tuning

Use trial and error to tune the backflush time. Reduce the backflush time to transfer fewer compounds to the analytical column.

1

2

3

Obtain a chromatogram in normal mode. Check out the retention times of the compounds you have to quantify.

Set the backflush time at the retention time of the last peak of interest.

Obtain a second chromatogram.

4

Adjust the backflush time (increments of 0.1 seconds are possible) until all components of interest are transferred to the analytical column and all unwanted peaks are backflushed.

Because a small pre-column is used, it is not always possible to cut between two adjacent peaks.

The

Backflush Time range is from 0.5 seconds until the maximum run time.

To disable backflush

To disable backflushing, set the

Backflush Time to 0. This puts the system in normal mode during the entire run.

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GC Channels

TCD Detector

Each GC channel is equipped with a thermal conductivity detector (TCD). This detector responds to the difference in thermal conductivity between a reference cell (carrier gas only) and a measurement cell (carrier gas containing sample components). The construction of a TCD is such that the changing thermal conductivity of the carrier gas stream, due to components present, is compared to the thermal conductivity of a constant reference gas stream.

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