Troubleshooting Guide

Troubleshooting Guide
Troubleshooting Guide - GC
Excessive Baseline Noise
Possible Cause
Solution
Comments
Injector contamination
clean the injector
gas lines may need cleaning
Column contamination
Bake out the column
Solvent rinse the column
Limit bake out to 2 hrs.
Bonded and cross linked phases
only
Detector contamination
clean the detector
noise increases over time, and not
suddenly
use better grade gases
usually occurs after changing a gas
Contaminated or low quality gases check for gas leaks and expired gas
cylinder
traps
Incorrect detector gas flow rates
adjust flow rates to recommended
values
consult literature
Leak when using MS, ECD, or
TCD
find and eliminate the leak
usually at the column fittings or
injector
Old detector filament, lamp, or
multiplier
replace appropriate part
use new part
Un-equilibrated detector
allow detector to stabilize
may require up to 24 hrs to fully
stabilize
Incompletely conditioned column
fully condition column
critical for trace level analyses
Change in Peak Size
Possible Cause
Solution
Comments
Change in detector
response
Check gas flows, temperatures, and
settings. Check background level or
noise
All peaks may not be equally affected. May be
caused by system contamination and not the
detector
Co-elution
Change column temperature or
stationary phase
Decrease column temperature and check for
appearance of a peak shoulder or tail
Change in the purge
activation time
Check the purge activation time
For splitless injection
Change in the
injection volume
Check injection technique
Injection volumes are not linear
Change in sample
concentration
Check and verify sample
concentration
Sample degradation, variances in sample
temperature or ph
Leak in the syringe
Use a different syringe
Sample leaks passed the plunger or around
the needle, Leaks are often not readily visible
Column
contamination
Trim the column
Solvent rinse the column
Remove about half to 1 meter from the front of
the column. Only bonded and cross linked
phases
Column activity
Irreversible
Only affects active compounds
1
Tailing Peaks
Possible Cause
Solution
Comments
Column contamination
Trim the column
Solvent rinse the column
Trim half to 1 meter from the front of the
column
Only for bonded and cross linked phases
Column activity
Irreversible
Only affects active compounds
Solvent-phase polarity mismatch
Change sample solvent
Install a retention gap
More tailing for the eluting peaks, or
those closest the solvent front
3 to 5 meter retention gap is sufficient
Solvent effect violation for splitless or
on-column injections
Decrease the initial column Peak tailing decreases with retention gas
temperature
lines may need cleaning
Too low of a split-ratio
Increase the split-ratior
Flow from split vent should be 20ml / min
or higher
Poor column installation
Reinstall the column
More tailing for the early eluting peaks
Some active compounds always tail
None
Most common for amines and carboxylic
acids
Retention Time Shift
Possible Cause
Solution
Change in carrier gas velocity Check gas velocity
Comments
All peaks will shift in the same direction by
approximately the same amount
Change in column
temperature
Check column temperature Not all peaks will shift by the same amount
Change in column dimension
Verify column identity
Switched column?
Large change in compound
concentration
Use a different sample
concentration
May also affect adjacent peaks
Leak in the injector
Leak-check the injector
Achange in the peak size occurs also
Blockage in gas line
Clean or replace clogged
line
Most common for split line. Check flow controllers
and solenoids
Split Peaks
Possible Cause
Solution
Comments
Injection technique
Change technique
Erratic plunger depression or having sample in
needle
Mixed sample solvent
Change to single solvent
Worse for solvents with large differences in polarity
or boiling points
Poor column installation
Reinstall column in the
injector
Usually a large error in the insertion distance
Sample degradation in the
injector
Reduce the injector
temperature
Change to an on-column
injection
Peak broadening or tailing may occur if the
temperature is too low
Requires an on-column injector
2
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