packing of the glassy carbon tube with gc chips may ?affect sample conversion if carrier gas flow would be so fast as to prevent meaningful interaction between sample, the graphite crucible and the gc chips.
Conversely, a too tightly packed gc tube may restrict carrier gas flow resulting in peak broadening and peak tailing.
Based on our experience, I recommend sieving gc chips to remove the fine grit and the large pieces leaving you with pieces that are 5 to 7 mm in size. On our system, for reactors packed for solid samples we set He to 1.45 bar to get a measured flow rate of 90 mL/min.
Keeping the GC column at 85C we got very good separation between H2 and CO (90 s peak to peak) and baseline separation between N2 and CO (66 s peak to peak).
Speaking of which and your problem, when is the last time you baked out your GC column (at 300C for 3 hours)? ;-)
Prof. Dr W Meier-Augenstein, CChem, FRSC
Stable Isotope Forensics & Analytical Sciences
Robert Gordon University
School of Pharmacy and Life Sciences
The Ian Wood Building
E-mail: [log in to unmask]
From: Stable Isotope Geochemistry <[log in to unmask]> on behalf of Osborne Malinga <[log in to unmask]>
Sent: 31 July 2019 12:39:44
To: [log in to unmask]
Subject: [ISOGEOCHEM] CO peak measurement
We acquired Delta V Plus Mass Spec with peripherals Gas Bench, EA and ConFlow IV from Thermo Fisher Scientific. The measurements of C, N and S Isotopes from compounds containing them, ranging from Biological to mineral, are perfectly done without any problems. When it was commissioned we did not have a CO cylinder as a result only Hydrogen Isotopes were successfully measured on Pyrolysis. Now we are having a growing need to measure both Hydrogen Isotopes and Oxygen Isotopes. From the very same bottom feed Pyrolysis tube we only see good peaks for Hydrogen Reference and sample but, when changing the Magnetic Focus to CO , we only see a good peak for a CO Reference and a tailing flat peak for the sample. There is also a problem with the separation between Hydrogen peak and CO peak of the sample. We have tried to sort out the problem of separation by lowering carrier gas flow which is Helium and we also tried to change GC Temperatures but we did not get the solution. We actual do not know whether the packing of the Glassy Carbon can be the problem. Please help.
With Best regards
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