Chromatography Forum

Hi All.

I'm being tasked with retrofitting a GC that was used previously with an MS (Brucker Scion SQ). The boss would like to be able to see H2, CO, and ethane in gas at ppm levels. I'm thinking TCD can accomplish this (N2 carrier gas?), but I have no idea on a column.

Thanks in advance for any advice.

Hi,

Sure, I set up a similar analysis up a couple of months ago. A Molecular Sieve 13X will do the trick. You will have to experiment with length a bit as the ethane may elute pretty close to the carbon monoxide. Restek has a great article online comparing the 5A and 13X for CO analysis, check it out.

http://www.restek.com/pdfs/59538A.pdf

You can also try a Molesieve 5X PLOT column. But it's a lot more expensive than a packed column.

Carrier can be either argon or nitrogen, and the TCD is fine.

"in gas" -- what is it in? gas phase, gasoline? If there is anything heavier than ethane present the molesieve will have issues.

I wouldn't ask a TCD to do ppm level, unless you mean hundreds of ppm.

Aidnai has a point.

Using a Molesieve PLOT 15m x 0.53mm ID and 50um film with a TCD, we got an MDL of 0.0020 mole % for CO. If you use a smaller sample loop you can also get away without a split injection and just use a GSV. Then ethane even in % quantities won't bother the CO peak.

The MDL will be higher with a packed column, but you can load a lot more sample. Depends on your objective.

We always use a 6-port valve to backflush a Molesieve, that's just a given. You will certainly kill your column if you get any heavies on it, and if you can't guarantee the sample composition, you're chancing it without the backflush.