Chromatography Forum

Dear all,
I'm quite new in GC technique. My problem is that I need to measure pCO2 using a GC, with concentrations at least down to 300 ppm.
Our seller suggest us to buy a molecular sieve column (5A, 0.53 id, 30 m lenght), but I am not really convinced about this choice.
Does anyone know how this column work with CO2 and eventually suggest a better one?

Thank you in advance for all the help you will provide

best regards
Daniele

Your seller gave you very bad advice.

CO2 is absorbed on a MS 5A column. It is not recommended.

If you wish to use capillary then you need a porous polymer column like Supel Q made by my company Supelco.

There are other manufacturers of similar columns.

But if you want to measure low levels accurately then you should not use a capillary column but a micropacked column or at least a packed column as they will allow a much larger sample capacity than you achieve with a capillary column and will allow you lower levels of measurement with better accuracy. (It is also a lot cheaper than a capillary but money is no object, right? )

Supelco makes the best micropacked columns. I would suggest a 'R' or 'N' polymer for the best separation of CO2 from air and methane-ethane with a 80/100 or 100/120 mesh. 1-800-359-3041 for technical advice, or 1-800-247-6628 to place an order.

A 2 or 3 meter 1/16" OD 1mm ID column should be adequate for your analysis with a flow of 5 to 20 mL/min.

A sample of 100-500µL is suggested for use with a TCD or a helium ionization detector. With a methanizer and a FID you will be able to measure extremely low levels, far below your probable needs, but this requires hydrogen carrier. Helium carrier is suggested with a TCD.

best wishes,

Rodney George
Senior Research and Development Scientist
Gas Separations Research
Supelco
595 North Harrison Road
Bellefonte, PA 16823

814-359-5737 voice
814-359-5459 fax
rodney.george@sial.com

Dear chromatographer1,
thank you very much for your fast reply. you confirmed my suspect, even if the seller continue to say that the column is ok to detect CO2, I will ask to another one.

I will also look for the column you suggest. Maybe in the next days I will ask you some other suggestions.

best regards
daniele