Problem with peak - CO, N2 with porapak Q

[marczmar]

I am using porapak Q column, peaks for N2 and CO overlap each other. Gas carrier is Hellium, I am using TCD. Could anyone help me with adjusting flow rate and temperature in order to solve this problem? If you think that it is impossible to achieve my goal with this column please suggest any other. I only add that the gas mixture where CO conc has to be determined is: N2, CO, CO2, H2.

[chromatographer1]

You have a good column but the wrong one for the mix you are trying to separate.

You should one of two columns:

A molecular sieve 13X or a Carboxen 1000.

You can use either helium or argon as the carrier gas. Hydrogen sensitivity is poor with helium.

The type of packed column is determined by the concentrations you are trying to measure and the type of detector you are using.

If you have to measure below 1000 ppm of hydrogen then a micropacked is suggested with a TCD.

The chromatogram below shows fixed gases (H2, O2/N2, CO, Methane, CO2) at 120°C using a 6 meter SS 2mm ID 60/80 mesh Carboxen 1000 column using He carrier at 30cc/min. (45 psi) 4% each with a nitrogen balance (200µL) Note the low response of hydrogen with He carrier.



If you email me I will be glad to offer suggestions.

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

[AICMM]

Marczmar,

I would suggest you keep the porapak Q and install a plot sieve as well. If you inject onto the Q followed by the sieve you can do the H2, N2, and CO then switch to the Q only and elute the CO2 so it does not get onto the sieve.

Rod is right, though, you are going to have a hard time seeing low levels of H2 with a helium carrier and a TCD. If you want to do really low levels of H2 in helium you will need a different detector or a different configuration.

Best regards.

[marczmar]

I would like to add that in fact I am not interested in receiving the rest of picks. However I mostly concern about seperation of N2 and CO and that is my main topic of invistigation

[chromatographer1]

If a big separation of CO and N2 is desired then a micropacked column with a TCD is shown below:

2 meter 1mm ID SS column packed with MS 5A 80/100 mesh is shown below: oven 70°C, 11cc/min. Helium carrier 100µL loop HP6890 µTCD



CO is at 1900 ppm Hydrogen is 1.25% O2 is 2500 ppm Methane is 1250 ppm

best wishes,

Rodney George
Supelco