GC-MS Oxygen separation from Methane

[zsoltiV]

Hi everybody,

I am new in GC-MS, I have an Agilent 7890A with a 5975C inert XL MSD with triple axis detector and a GS-GasPro 113-4362, 60m x 0,32mm column. I want to separate oxygen from methane with this GC-MS system. I have a calibration gas with 70ppm of O2 and a Methane balance. Can anybody send me how to setup my GC and MS to find O2. Is it possible to separate O2 from Methane??? Thanks a lot.

[rb6banjo]

It looks like subambient oven temperature to start might be your only option on this one (if your'e tied to that column):

http://www.chem.agilent.com/cag/cabu/pdf/c762.pdf

Even at RT, you likely won't be able to get there. They can't even separate methane from N2 at 25 °C:

http://www.chem.agilent.com/cag/cabu/pdf/gaspro.pdf

On a molecular sieve column, N2 comes out after O2. How complicated is your matrix? Do you have other analytes of interest for this method or is it just oxygen and methane? To do this one, I would have chosen a molecular sieve column and a pulsed-discharge helium-ionization detector. However, that combination won't work well if you are after lots of heavier materials.

[zsoltiV]

Thanks for reply I will use the subambient oven temperature. I called to guys from Agilent for the price a method how to get the subambient oven temperature. They told that I need only a valve for CO2 and CO2. I think this wil l be our solution. I want analyze natural gas from C1 to C8 + CO2, H2, O2 and N2.

[rb6banjo]

Interesting that they have a LCO2 option for oven cooling. I didn't know that. Be careful about flooding a closed space with CO2. You don't want people asphyxiating in your lab! CO2 is heavier than air. My GC's that can go subambient use LN2. I don't use it often.

Use of either LN2 or LCO2 could cause you problems as "false positives" in your analysis. Both of these coolants are on your analyte list.

[Adam Howard]

This kind of gas analysis requires a PLOT column and subambient temperature program. If you don't need automation, you can achieve lots of cooling using dry ice in the oven.

A true cryogenic setup running off a nitrogen Dewar is much more elegant, but the dry ice trick might assist your method development.

A GS-GASPRO column will easily do that separation going subambient.

[mckrause]

You don't actually need any separation for that mixture. O2 and methane give you quite different mass spectra, so you can use the MS to provide you with the separation you need. Any separation the column provide is just gravy.