Chromatography Forum

Hi

I'm really stuck

I have been trying to separate CH4, CO2 and N2 to analyse the CH4 levels. I am using a Restek Q pak and Restek 5A sieve columns http://www.restek.com/pdfs/59538A.pdf with a FID.

Both of these columns say they should separate methane. However in each case I find that both the CH4 and N2 peaks are directly on top of each other at about 6 minutes on one and 9 on the other! I have double checked this several times by running calibration gases.

I have tried lowering the column temperature, raising the carrier flow and increasing the split but nothing seems to improve matters.

Edit:
I forgot to say what settings I have been mainly using

50 deg column temperature
10ml/min N2 carriers gas
Split of 20:1
Injecting 500 microliters of gas

I dont understand why this is happening with both columns, can anyone help?

Many thanks

Matt

Please explain how you are splitting with a 2mm ID packed column !

Then tell us how you are getting N2 to detect using a FID detector.

Rod

Hi

I am a very new user to GC so forgive me if i've stated the wrong information. There is no one who can train me around so Im learning as I go. The software has a setting for the "split" so I have included that parameter, it may not be doing anything based on what you say.



Anyhow I have resolved the peak problem myself in that I am also the cause!!

Methane was being retained in the regulator valve as I had not flushed it out meaning when I ran pure N2 I consistently saw a residual peak of methane that I assumed was N2 being that N2 dosent produce a peak (as you point out). I drew the conclusion that the peaks were overlapping.

Dumb I know but I dont have anyone to sound this stuff out with

Thanks anyway

Matt

Matt

The example you gave was using 2mm ID columns. You are probably using capillary columns.

I understand you are learning, and my questions were only to get you to give a bit more information.

Yep, got to flush that sample loop. You are right, and I am glad you found the mistake.

It is also good you learned that nitrogen is not detected by a FID.

We all have things to learn. I hope I did not embarass you TOO much.

Welcome to the world of chromatography and all there is to learn.

You got your feet wet. Keep at it and you will survive.

Good luck, and best wishes,

Rod