Molsieve Separation for O2 and N2

That is a possibility.  Can you provide more details?  Which specific mole sieve column?  Any pre-column?  Which carrier gas?  What was the column temperature when it worked and when it didn't?  Can you provide chromatograms showing both runs?

Dear Lance, Thanks for your response. We have 3 packed columns, 4 ft hayesep Q precolumn, 10 ft Hayesep Q analytical column and 10 ft 13X Mol Sieve column. The temperature program looks fine. The real issue we noticed is, initial runs are perfect, after  a few runs, O2 peak area keep on coming down and a hump started appearing along with H2S peak. We couldnt find any leakage in any of the valves. We have tried saturating the Hayesep Q analytical column with pure Oxygen runs based on the advice from one the forum response. Kindly advce.

Are you using hydrogen carrier?  Water tracks close to H2S on a Q column so I'm wondering if there is a reaction of some sort happening on the column.

Hi,

Are you analyzing a hydrocarbon gas mixture?  I have noticed on some mole seives that if you have Iso-butane and Iso-pentane in the sample analyte they can elute out in an odd large hump in the middle of the molesieve and swallow up the O2 peak.  Do you loose your O2 peak on all samples or on some samples or even standards. 

HI,

Could you fix the problem?

Best Regards,

Increasing the temperature before the separation is done will definitely decrease the resolution, but this sounds like a  leakage problem where a bit of moisture (or any other polar component) will change the mole sieve column's selectivity. To give better advise we would need a list with all components analyzed and the temp. program. And seemingly the switching diagram.

If you flush the complete system with oxygen at high temperatures, you will oxidize the Q phase partially and get all kinds of polar components coming off (up to benzaldehyde).