Hi
I'm looking for a solution of my problem. I want to measure CO and CO2 in the range of 1-20 vpm with a HP GCD and a PoraPLOT Q (25m x 0.53mm id - with a uncoated 0.1mm id column immersed about 2m in PLOT for split interface to MS).Sample matrix is a mixture of permanent gases. My problem is that I can't resolve the N2 and CO peaks.

Does somebody have an ideea ?
I will be very thankful.

Thank You

There are a number of problems here. First, the separation of N2 and CO would be difficult on a PoraPlot-Q type column at normal GC temperatures. You would be better off with a 0.53-mm i.d. x 25 um film CP-CarboPlot P7 column (from Varian/Chrompack: click here to go to their product description, click here to see an example chromatogram from their CP-Scanview CDROM) or a molecular sieve 5A column.

Second, your homebrew GC/MS split interface may broaden the peaks and loose resolution of the N2 and CO peaks. You should use a commercial MS split interface for this purpose.

Third, you will have difficulty with background N2 in the mass spec due to air leaks, especially with a homebrew interface. Be sure to eliminate as much of the air background as possible. Obtain a can of hydrofluorocarbon dust-off, normally for photographic or electronic use, and waft a little of the gas from it onto your GC/MS fittings while monitoring the mass spectrum. If there's a significant leak, you'll see mass peaks appear corresonding to the hydrofluorocarbon.

Thank you John !

You are a treasure of informations.

Thanks again.