Toubleshooting the Gas Chromatograph

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GC troubleshooting

Peaks and background noise etc.

Troubleshooting the Gas chromatograph

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Excessive baseline noise

Change in peak size

Tailing peaks

Retention time shifts

Split peaks

Excessive Baseline Noise

Possible Cause Solution Comments

Injector contamination clean the injector gas lines may need cleaning

Column contamination Bakeout the column
Solvent rinse the column Limit bakeout to 2 hrs.
Bonded and crosslinked phases only

Detector contamination clean the detector noise increases over time, and not suddenly

Contaminated or low quality gases use better grade gases
check for gas leaks and expired gas traps usually occurs after changing a gas cylinder
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 crosslinked phases
Column activity Irreversible Only affects active compounds

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 crosslinked 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 temperature Peak tailing decreases with retentiongas 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 Comments

Change in carrier gas velocity Check gas velocity 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

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