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Study Notes: GC Troubleshooting

The technique of GC is inherently complex with many pieces of equipment interacting to analyse a sample and to produce a chromatogram as a result. In such a system the potential for things to go wrong is necessarily high if operators do not know what they are doing or are less than careful in their approach to the work.

But even for experienced and meticulous technicians things can and do go wrong! This is where the ability to ‘troubleshoot’ is important.

The following table contains examples of errors/malfunctions and the likely appearance of a chromatogram under these circumstances. These examples will be useful when you work with the virtual GC.

Symptom Possible cause Checks
1. No Peaks.

No carrier gas.

Injector temperature too cold sample condensing.

Syringe is blocked.

Septum is damaged.

FID flame out.

Check carrier gas supply.

Check injector temperature versus that stated in method.

Replace syringe.

Replace septum.

Check air/hydrogen supply and re-ignite flame.

2. Poor sensitivity with normal retention time.
GC trace - poor sensitivity with normal retention time

Attenuation too high.



TCD filament temperature too low.

 

Check attenuation and compare it too that stated in the method.

Check filament temperature and current and compare too method.

 

3. Poor sensitivity with an increase in the retention time.

GC trace - poor sensitivity with an increase in the retention time

Carrier gas flow rate too low.


Injector septum continuously leaking.

 

Check arrier glow flow rate pressure.

Replace septum.

4. Negative peaks.

GC trace - negative peaks

Polarity switch in wrong position (TCD). Check test method and polarity position.

5. High background signal (noise).

GC trace - high background signal (noise)

Contaminated column or excessive bleed from the column.

Carrier gas flow rate too high.

Carrier gas flow leak.

Hydrogen flow rate too high or too low (FID).

Air flow too high or too low (FID).

Re-condition column.

 

Check carrier gas pressure.


Check carrier gas pressure.

Check pressure of Hydrogen supply.

Check pressure of Air supply.

6. Tailing Peaks.

GC trace - trailing peaks

Column oven temperature too low. Check oven temperature to that stated in the test method.

7. Leading peaks.

GC trace - leading peaks

Sample condensed in the system.

 

Ensure injector and detector temperatures are correct.

8. Unresolved peaks

 

GC trace - unresolved peaks

Column oven temperature too high.

Carrier gas flow too high.
Check test method and adjust oven temperature accordingly.

Thoroughly flush syringe and repeat injection.

9.Extra Peaks.

GC trace - extra peaks

 

Residual material from previous sample.


Dirty Sample.

Contamination syringe.

Allow sufficient time for the previous sample injections to be eluted.



Thoroughly flush syringe and repeat injection.

10. Sudden drop-off of a normal peak.

GC trace - sudden drop-off of a normal peak

Loss of hyrogen or air.


Carrier gas flow rate too high.

Check hydrogen and air pressures.

Check carrier gas pressure to that stated in the method.

 

It may be useful for you to print a copy of this for troubleshooting activities.

Note that there may be other errors/malfunctions that may occur.

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