Column select for permanent gases / CO2

Question

We have put in service a 'select permanent gases /CO2 plot GC column' from Agilent

Here is the description of this special column "Select Permanent Gases/CO2 is a set of two parallel columns that combines CP-Molsieve 5Å for permanent gas analysis and CP-PoraBOND Q for CO2 analysis. Column dimensions meet the need for fast separation, lowest level analysis, and quantification of argon/oxygen. The Select Permanent Gases column separates permanent gases and CO2 in a single run, and columns are coupled, tested, and securely mounted on the EZ-GRIP column mounting system"

The detector is an FID, the GC is 6890, the software is Chemstation rev. B. Carrier gas is Ar.Oven is # 60°C.No ramp.

When we inject pure CO2 on this column we get 2 peaks. The second peak is clearly identified as peak from CP porabond. But I dont understand the first peak of CO2?? eluting from the Molsieve ? The area of both peak are in the same order of magnitude.

We have eliminated double injection possibility

By the way analysis of all other geses is correct : N2, O2, CH4, CO

Any suggestion from the community ?

Thanks

Dr. Know · Accepted Answer

Hi Cecile,

a Select for Permanent Gases was developed for the analysis of air samples, nothing with CO2 concentrations above 1000 ppm. When you inject pure CO2 you saturate all active sites of the molecular sieve column and the remaining CO2 comes off the column as if it was just tubing-one single peak. And there are not so many active sites in the molecular sieve, therefore your peak area is comparable and only influenced by the response characteristic of your detector.

To analyse gas impurities in CO2 I advise column switching techniques (valve or CFT) like described in our application note A01272.

If you stay with the Select for Permanent Gases, you will need to condition the column often.

Best regards,

Norbert

Column select for permanent gases / CO2

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