Chromatography Forum

I am currently running a 30m column that is split at the end with a 3 meter at 0.25 retention column going to FID and a 10 meter retention column at 0.1 going to MSD. I'm running into an issue with high N2 levels at around 35-40% and O2 at ~10-13%. Moisture and CO2 are low. The MSD is pumping down and is fairly steady. Is this normal for a MSD that also is venting to enviroment, or am I going to be cleaning every month?

Thanks

I am currently running a 30m column that is split at the end with a 3 meter at 0.25 retention column going to FID and a 10 meter retention column at 0.1 going to MSD. I'm running into an issue with high N2 levels at around 35-40% and O2 at ~10-13%. Moisture and CO2 are low. The MSD is pumping down and is fairly steady. Is this normal for a MSD that also is venting to enviroment, or am I going to be cleaning every month?
Thanks

Nor this, nor that.

You have got leaks on joints of column with restriction tubings - probably.
Or/and MSD sucks N2 and O2 from FID through your 3 m restriction tubing.
As diagnostic measure, increase carrier gas flow through column and check N2 and O2 levels.

Leaks at the split point are the most likely problem - what kind of connector are you using ?

To check for backflow from the FID compare the oxygen levels with the hydrogen and makeup flows to the FID on and off - if there is back flow (or back diffusion) you will see less oxygen with the gasses on.

Peter

Don't forget butane from gas lighter when inspecting split connector.

I think it's due to the connectors. If the vacuum could suck N2 & O2 from the FID, you would not see a peak of the detector.