Detection of oxygen with TCD

[vksharma]

WE are having one NGA having the configuration of Porapak and molecular seive columns and TCD. We are facing a unique situation in the detection of oxygen. If we inject (manually) room air the peak area ratio for the first injection comes as oxygen (15%) and nitrogen (85%). for next air injection the ratio changes to 19% and 81% respectively. for the subsequent injection the ratio remains constant. However if we inject a natural gas (C1 to C8) analyse it and then again inject room air the peak area ratio reverts back to 15 % and 85 % .
Is this problem related to columns or TCD?
What is the maximum conc of oxygen that can be detected by TCD accurately?
Is there any solution to this problem?

[chromatographer1]

The problem sounds like the column. MS can be problematic unless the column is made properly.

Your questions:

"Is this problem related to columns or TCD?"

columns

What is the maximum conc of oxygen that can be detected by TCD accurately?

Given the proper technical parameters, 100%.

Is there any solution to this problem?

Yes, there is.

Sorry I can't give you more but I solve problems for a living and don't want to give away the farm for free.

and to all you complainers that this is a free forum, you are right. So I can shut up completely, or at least point in the right direction. Which do you prefer?

best wishes,

Rodney George
consultant

[AICMM]

vksharma,

Are you running with a scrubber on your carrier gas? Also, what happens if you bake your sieve?

Have you searched the site, there are a number of comments on the use of molecular sieves that could prove useful?

Best regards.