Chromatography Forum

hi guys
i am starting to use porapak q column with tcd detector to analysis permanent gases like CO2,CO,CH4,H2,N2 but in my experience i can only see 2 peaks not anymore!
analysis condition :
tcd temperature: 80c
column temperature: 35c
injector temperature: 50c
carrier gas(argon):20ml/min

what can i to do for this problem?!!

It's not clear to me. Do you only see 2 peaks? If yes, which 2?

I went to Restek's website (www.restek.com), searched the chromatogram database for your analytes and it only showed one column suitable for your analytes. Shincarbon ST. Resolution of O2 and N2 under their conditions was not fantastic so if you have a lot of one or the other in your sample, it may not work for you.

I found a side-by-side comparison of Shincarbon and PorapakQ on the Shimadzu website and it indicates that the Shincarbon might be a better option. Good luck!

Your two 'peaks' are as follows.

peak 1 CO,CH4,H2,N2
peak 2 CO2

The best column to separate CO,CH4,H2 and N2 is a molecular sieve column. However, this column will absorb CO2. The usual way to analyze this type of sample is to use the two columns with two valves. One valve injects the sample and the other is configured to isolate the mol sieve column. You inject the sample into the Porapak Q column where CO,CH4,H2 and N2 will pass through quickly into the mol sieve column. The mol sieve column is then isolated, allowing the CO2 to elute and bypass the mol sieve column and go to the detector. The mol sieve column is then switched back into the carrier gas stream allowing H2,N2, CH4 and CO to elute in that order.

The post above mentioned Shincarbon. You should look at the following web site which gives chromatograms on Shincarbon columns.

http://www.hichrom.com/assets/Products/ ... N-ST_E.PDF

Gasman