FID chromatograms

[alba]

Dear all,

I'm trying to detect CO, CO2 and CH4 from air with 2 sample loops, a methanizer and an FID detector.

I have been doing some tests according to a runtime table that other people have been using but I cannot obtain any peak at all (only those associated to valve changes and two wide ones at 0.5 and 4.4 min…).

To try of figure out what the problem is and as a first step, I have done tests to detect only CH4 through the FID (without using the methanizer; I am suspicious about the catalyst of the methanizer...), but I cannot find the peak of CH4 by using only the FID neither (TESTS 2 and 3 in the attached link).

http://albabloc-fr.blogspot.com

Could anyone give me some insight about the type of chromatograms that I have obtained? Could I smooth/reduce the signal associated to valves changes? Do you know the meaning of the peaks at 0.5 and 4.4 min?

I'm learning step by step about these type of systems... Sorry if I ask/show basic data/info.

Thank you in advance for your help.

[AICMM]

alba,

You are on the right track trying to do just methane first, since this eliminates the methanizer as an issue. However, you need to tell us what columns you are using and what flow rates you are using. It would also be useful to know how your valve is configured (I would guess you have a switching valve since you are trying to do CO and CO2.)


Best regards,

AICMM

[mmmargaret]

You can also try doing manual injections with a gas tight syringe to see if the sampling valve is an issue.

[alba]

Hi,

we are trying to reproduce the configuration presented in this paper:

http://www.atmos-meas-tech-discuss.net/ ... 1-2009.pdf

The microECD section is not a problem for us but, as shown in the chromatograms that I mentioned in the previous post, the FID is giving us some problems. For the FID section:

Columns are the following ones:
Col. 3 --> Porapack Q, 1/8" o.d.
Col. 4 --> Molsieve 5A, 1/8" o.d.
Col. 5 --> Haysep Q, 3/16" o.d.

There are several valves in the setup, as you can see in the link. The flows for the carrier gas are (or should be):
Aux. 3 (N2) --> 55 mL/min
Aux. 4 (N2) --> 67 mL/min
Aux. 5 (N2) --> 29 mL/min

(we checked the flow at the beginning of the line (before the columns), but I think that we did it wrong and that we should do this measurement at the detector, am I right? Should we check the flow at the detector considering all the valves positions?)

Is the baseline too high? What could be the meaning of the wide 'peak' at around 4.4 min? The peak associated to valve changes, could they be reduced somehow?

We are having also some problems with the flame of the FID, it blows out only after several injections. He have had to change the Lit offset parameter to a value around 1.2. How can this affect our measurements with the FID? Should the FID be checked if this problem persists?

I really thank you in advance for your help.

[alba]

Dear all,

we have already found the problem: there was a leak!!! so the sample was not arriving to the detector!!! We have also changed the ratio between air and H2 (450 to 90) and now the flame doesn't blow out after several runs (I hope it lasts for long).

We have still a little problem:

when trying to obtain a nice peak for the CH4 (sample loop 3) detected after CO (sample loop 2), we have some problems because we do not get it well separated from the O2 "peak" that we also see (we have not adjusted yet the time in order to not see the O2 going through the methanizer, although we know that this should not arrive to the detector).

We have done a test at a lower oven temperature (from 72ºC to around 60/62ºC), and we obtain a better peak. We are considering programming an oven ramp temperature because for CH4 and CO (sample loop 2) we get better results at 72ºC.

What do you think about this approach? Do you think that this is a good idea? Would you suggest another approach?

Thanks a lot in advance,