I've sorted through the archives and see a lot of troubleshooting of rising mass
30 during EA-IRMS but I am having some issues with mass 30 spiking up at
the end of a GC-IRMS nitrogen run and then slowly decreasing.
The issue started with a routine reoxidizing of the oxidation reactor, after
which there was the normal excess of 30 which was removed by solvent
injections. But once mass 30 was gone, I still was unable to get nice mass 28
peaks with my standard. They were all just blips. We have a quadrupole
mass spec in parallel with our IRMS so I know that the compounds were
coming out of the GC column just fine. So we replaced the reduction reactor.
No real improvement, peaks barely discernible. There was a lot of water in
the system so we thought maybe it was building up in the capillary and
blocking the compounds (is this possible?) so we ran in carbon mode to make
sure there was no blockage (carbon was fine). So over the weekend I made
sure He flow was high to purge the system of water.
Then we had a power outage (thunderstorm + building UPS failed) and I came
in the next day and the turbos were off. So of course it took a few days to
get the water out of the system. Now, I am seeing mass 28 peaks in the
beginning of the run, but then I get a rise in mass 30 near the end of the run,
and don't see any of the mass 28 peaks I should see. Running a blank of just
my solvent didn't yield a mass 30 peak.
Does this make any sense to anyone? Not sure what to do next...