Chromatography Forum

Dear all,

we're setting up a GC with a FID and we are getting very high FID signal values. We get these results:


1- [Zero air (generator) + trap] + [H2 (cylinder) + trap] --> 260 pA

2- [Zero air (generator) + trap] + [H2 (cylinder)] --> 67 pA

3- [Zero air (cylinder) + trap] + [H2 (cylinder)] --> 65 pA

4- [Zero air (cylinder) + trap] + [H2 (cylinder) + trap] --> 267 pA

It seems like the trap from the H2 (Molsieve 13X) source is making the difference.

What would you recommend us to do? Should we leave the GC for a long period of time and see if this value changes? We left it for one night with configuration #1 and the signal diminished a little (from 330 to 260 pA)...

Thanks in advance for your help!

Activated charcoal traps to remove organincs make most sense on an FID - it is robust to trace cases and moisture, but will give a high background signal if organics are coming in with the gasses.

The readout from the FID when no sample is passing through the detector is the baseline, not the signal. The signal is what you get when a peak is eluting.

Peter

Take the trap and connect it to clean gas and condition it at 300C for a day.

(I assume it is metal and can be so treated.)

Then reconnect it into your system and see what you get.

best wishes,

Rod

Condition or change the trap. Is there actually any benefit to having one in line ? If your H2 spec is 99.999, what impurities are listed ? Running for FID even a small impurity of Hydrocarbon will make little difference to the signal. I prefer to run without traps as problems with connections and trap life cause more problems than they stop.

I would check that the detector is clean.

Do you have the correct jet installed for the column you're using?

Dear all,

we conditioned the trap at a temperature of 300ºC and now the baseline is 35 pA! Considering that we use a very high flow of H2 (90 mL/min) which passes first through a methanizer, this is a good value for us.

Thank you for your replies!

Dear Alba,

Thanks for the end of the story. So many lack the grace to do this. We all appreciate your sharing the happy ending.

And congratulations on discovering the happy ending.

best wishes,

Rod