GC-FID Noise

[Axar]

Hi!!!
In our laboratory we have one GC-FID and two HPLC systems placed in the same room. GC's signal is too noisy (approx. 1 hundred pA).
Does volatile compounds of HPLC's mobile phase can couse that noise?
Thanx!

[Peter Apps]

Not unless there is something badly wrong with the GC. When you say noise do you mean a constant standing signal or a fluctuating baseline ?

Peter

[Axar]

I meant constant signal.
I tryed different columns, carrier gases and flow rates. The signal was same.
Also I tryed different liners and jets.

[Peter Apps]

You have invested a lot of troubleshooting effort. What happens if you autozero the detector ?

Peter

[chromatographer1]

You can also manually zero the electrometer of the GC to bring it to zero.

Rod

[Axar]

I guess that autozero is not an option, because base line fluctuates in long term. Some times it is 80 pA some times it is 120 pA.
If I autozero it at 120 pA, FID will report flame out. (that is my suggestion, I have not tryed that).
I work at state analitical laboratory, so it is essential to obtain infalliable results. If I obtain a negative result on a product, the produser may sue my lab and it will be very comfortable for me to be sure in my results it that case.
If you ensure me that it is not affect sensitivity, I will stay calm and continue my work.
As I said before, I suspect volatile compounds of HPLC's mobile phase.

[chromatographer1]

If you have cleaned your detector and the signal is still HIGH then you may have contamination in one of your gas supplies.

The air and hydrogen must be clean. Since the signal varies (but otherwise the detector seems to be working normally?) that means your contamination is varying. Are you sure it is not column bleed?

Change out cylinders or put new traps on your gas supplies. Is the signal 'noisy' or is the output smooth?

It sounds like you have someone with experience look at the GC, whether it is a service person or a chromatographer from other group.

You could be having an electronic problem as well.

Too bad you can't show us a chromatogram expanded to show the noise level and the output level.

best wishes,

Rod

[Axar]

If you have cleaned your detector and the signal is still HIGH then you may have contamination in one of your gas supplies.

Yah! I also suspect that.

The air and hydrogen must be clean. Since the signal varies (but otherwise the detector seems to be working normally?) that means your contamination is varying. Are you sure it is not column bleed?

Change out cylinders or put new traps on your gas supplies. Is the signal 'noisy' or is the output smooth?

I'll try to find new traps and report you results. I used different capillary colums. Most of them was new and hadn't shown such bleed at other GCs. Signal output is hight, flucluating in a long term baceline. The word "noisy" is not correct - my fail. It is smooth enouth to recognise peaks of analites.

It sounds like you have someone with experience look at the GC, whether it is a service person or a chromatographer from other group.

There are only two persons, experiensed with GC in our organisation - me and my supervisor. The servise person could not help us.

You could be having an electronic problem as well.

It is the worst option, so I wish to don't think about it right now.

Too bad you can't show us a chromatogram expanded to show the noise level and the output level.

best wishes,

Rod

I'll try to download pictures for you tomorrow. Thank you all very much!!!

[chromatographer1]

If the problem arose at the same time you installed a new column................... well, why state the obvious.

Have you tried a different column to see if the signal still stays high?

Remember that if your pneumatics are contaminated from a bad supply of gas it may take a while for all the contamination to pass through the system. I have had this happen in the past and it is a royal pain to fix, but it can be done.

best wishes,

Rod

[Axar]

I performed different methods with different columns (both old and new). The problem was same. In addition there was a little finding: I'm not sure, but when I use conditioner in my room hight of base line seems to be lower.

[aldehyde]

Remove the column and troubleshoot only the FID. Block off with a column nut and an inch of column+septa or something. Have you measured the flows? You mentioned filters, do you have existing filters or is it just tank-tubing-instrument?

If the flows are wrong the lines or pressure controller have likely been plugged up with contamination. If you have really old filters they would be just giving off constant contamination rather than holding it back. You could remove the filters and connect the gas supply directly to the instrument (with new tubing).

Have you changed gases lately? New tank? If the problem is sudden it could easily be a badly contaminated tank, but if it has come over time it would be caused by using gases that arent of high enough quality.

[Axar]

Here you can see my problem.
Temperature of oven was common (around 60C). Carrier gas flow wasn't too strong.

[chromatographer1]

This looks more electrical than sample contamination. Time to clean the electrometer contacts, and the slot on the motherboard of the GC. The detector insulators and all wiring contacts should be cleaned and checked.

Good luck,

Rod

[Peter Apps]

Do you really have a problem ? As far as I can see you have about 0.5 pA of rapid noise, and about 0.3 pA of drift in the short term. You mentioned that you have a much larger long-term drift, does this happen with the column at a constant temperature, or only when you temprature programme. Upwards drift during programming is to be expected.

The approx 140 pA of standing signal will disappear if you autozero, and this is so simple to do that I really think that you should try it.

The sensitivity of the noise to room temperature is a concern, and points to crud in gas plumbing bleeding off quicker when the room is warm.

Peter

[Axar]

There are 2 hours between first, second and third injections. That time we used used column. Column was stored properly, preventing O2 to harm stationary phase. Thereby baseline height had changed more than at 10% during 4 hours. That is what, that makes me worry.