Chromatography Forum

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?

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

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.