You have to prevent the air peak from entering the source, otherwise it will trip..
I do it by only activating the open split during the CO2 peak, take enough time for a good background preceding the CO2 peak, about 10 seconds should be enough if you use individual background (5 sec). You will still see a small trace of mass 46 on the position of the air peak. I fill an Exetainer with helium and inject some CO2 to figure out where the CO2 peaks are, in that way I can make the event table for OS in and out..
Also be sure that N2O ( if you have any produced by your soil..) it separated well from CO2 as it has the same mass but very different isotope ratio.
Richard van Logtestijn
Department of Ecological Sciences
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From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Katerina Jandova
Sent: dinsdag, februari 07, 2017 23:32
To: [log in to unmask]
Subject: [ISOGEOCHEM] soil respiration samples using GasBench
I'd like to measure 13C/12C in CO2 in samples of soil respiration. Can the samples be directly forwarded via the PoraPlot GC column of GasBench to open split and mass spec? Or are any components of the air (e.g. molecular oxygen) prohibited from entering the mass spec and need to be separated out using the LN (cold) trap?
Any advice would be most welcome.
Katerina Jandova, Ph.D.
Institute for Environmental Studies
Faculty of Science, Charles University
Benatska 2, 128 01 Prague 2