Chromatography Forum

Hi all,

We have faced recently a problem with the DEFC in our GC CP3800, varian model and was replaced with new one, newer model.

The GC was started for conditioning then taken into service but unfortunately we found that the FID channel was not able to show any peak for our standards or samples.

We've checked all what we have doubt about, everything was as before that problem.

BTW, the problem was happened due to a high pressure coming from the outlet of Hydrogen cylind due to regulator failure.

looking forward any kind of help

regards,

Alchemist

You need to measure all the gas flows to the detector with an independent flow meter, not the on-board EEFC, which might have been damaged by the high hydrogen pressure.

Does the FID ignite ? - check for condensation on a cold shiny surface.

Have you tried switching off and back on again ?

Peter

You need to measure all the gas flows to the detector with an independent flow meter, not the on-board EEFC, which might have been damaged by the high hydrogen pressure.

Does the FID ignite ? - check for condensation on a cold shiny surface.

Have you tried switching off and back on again ?

Peter

Thanx Peter for your response,

Actually, we've checked all the flows going to GC as well as the hydrogen/air ratio and the FID flame as well. We found that the flame is working well and the status of the GC showing ready but when we inject sample or standard, no peaks detected on FID while TCD is working fine as dual channel.

We have different methods using FID, we tried it all even liquid method on FID as well but the result were the same, no peaks detected.

regards,

Please post details of the dual channel arrangement.

Have you confirmed that you have carrier gas flowing to the FID ?, turn off all the flame gasses and measure the flow coming through the column.

Do you see any response on the GC front panel signal readout when you do a GC run ?

Do you see any response on either the front panel or the data system if you wiggle the detector signal cable ?

Peter

Just a thought:
Did you check if the signal is set to FID?Like Signal A and B to front and back detector.Since you're working with 2 detectors it can happen that signals are not correctly set to each detector. This could justify the peaks absence and also the fact that you don't have any error message.
Regards,
At_om

Please post details of the dual channel arrangement.

Have you confirmed that you have carrier gas flowing to the FID ?, turn off all the flame gasses and measure the flow coming through the column.

Do you see any response on the GC front panel signal readout when you do a GC run ?

Do you see any response on either the front panel or the data system if you wiggle the detector signal cable ?

Peter

Acually i didn't try to note the signal readout on the front panel while having a run, but what i've seen that there is signal readout but no fluctuation in that signal during the run.

But what i've done that i tried to inject some methanol on the top if the flame just to see the response of the signal manually.. it was okey.

regards

Just a thought:
Did you check if the signal is set to FID?Like Signal A and B to front and back detector.Since you're working with 2 detectors it can happen that signals are not correctly set to each detector. This could justify the peaks absence and also the fact that you don't have any error message.
Regards,
At_om

thats has been done

Alchemist,

As Peter notes, you have to tell us about dual channel. If dual injectors columns and injectors it does nothing for troubleshooting. If dual columns and detectors sharing the same injector it will prove very useful.

You have proven out the detector, now the data system and the injector. Monitor the baseline in the software (tell it to run using an empty vial) and inject the methanol in the detector again and see if the data system picks it up. If yes, then focus on column and inlet. On another run, inject some appropriate solvent on the front of the column (right after the injection port) and see if the run picks that up. Then we go from there....

Best regards.

Alchemist,

As Peter notes, you have to tell us about dual channel. If dual injectors columns and injectors it does nothing for troubleshooting. If dual columns and detectors sharing the same injector it will prove very useful.

You have proven out the detector, now the data system and the injector. Monitor the baseline in the software (tell it to run using an empty vial) and inject the methanol in the detector again and see if the data system picks it up. If yes, then focus on column and inlet. On another run, inject some appropriate solvent on the front of the column (right after the injection port) and see if the run picks that up. Then we go from there....

Best regards.

Hi again,
Actually the dual channel are using the same injector for LPG and gas samples and that we are using the FID for LPG samples while FID/TCD fo gas samples. Another injection port is for liquid we tried it as well, the result that the FID was not showing and peak of any of the injected samples at all while TCD is showing for gas.

alchemist,

Neither of your FID's show a signal on the data system but your TCD does? Do I have that right?

Best regards.