signal/detector problem

[PaulinaGu]

Hi,

Yesterday I run out of Air and the new cylinder wasn't replaced till this morning. Trying put the run on GC TRACE I realised that peaks are much smaller (like 1% or less from the peaks seen before for the solutions analysing the same compound).

I have got two GC TRACEs and this happened on both machines.
I have got in the lab other GC's that works fine.

I believe that there is some kind of problem with the detector on GC TRACE.

Did someone have the same problem in the past?

Please help.

Best regards,

Paulina

[dblux_]

Hi Paulina,
Presumably your detector was FID. I don't thing FID could be damaged or deteriorated when you ran out of air. The flame has probably extinguished due the lack of oxygen.
Check current flows of gases.

[Peter Apps]

Like dblux says; running out of air cannot damage the detector itself, but it would trigger a flame out alarm that would shut down all the gasses to the detector. Probably the gas flows have not been properly restored. Check gas flows and re-ignite the flame. Depending on the alarm settings on the GC some hot zones my have cooled.

Presuming that the other GCs are using the same air as the Trace GCs there is nothing wrong with the air now.

Peter

[PaulinaGu]

Thank you both for quick response. The detector I'm using is an FID. I do have other 5 GC on the same gas lines that works fine just 2 Traces GCs are having problems.

I did try to reignite the flame and I check the flows on GC for make up gas. Everything looks like it should to be honest but when I'm injecting some solvent that before gave me huge peak (hight around 10000) now the same solvent peak give is 100 high at the same RT. RT didn't change.

Thanks for any suggestions.

[dblux_]

... and I check the flows on GC for make up gas...

What about hydrogen and air flows, do they stay unchanged ?
Check whether the FID jet isn't partially clogged.

[Peter Apps]

Hi Paulina

The solvent peak is not the best one to use to judge detector response since it is almost always off scale, and is very vulnerable to minor changes in inlet conditions.

You need to compare a real sample or a test mix from before the air ran out to now.

Peter