Nitrogen level in GC-MS

High nitrogen without oxygen is not a leak.  Well, it could be a leak before a gas trap that is scrubbing the oxygen out.  Is your indicating GasClean filter showing oxygen contamination?

Does your system have a Helium Conservation Module installed?  This module runs nitrogen through the system during standby or sleep. Do you use Sleep/Wake modes? 

Gas Clean filters are shipped packed with nitrogen.  Sweeping the nitrogen out after installing the trap can take some time.  On slide 5 of (+) How to Change Your Helium GCMS Carrier Gas Tank - Two ways - Files - GC/MS - Agilent Community it shows how to pressurize/depressurize to remove residual/trapped air. This same process helps remove nitrogen in the trap material.

Hello Paul,

first of all, thanks for taking your time on replying. Answering your questions: the GasClean filter does not indicate oxygen contamination (it has a little portion of another color, meaning there is a litlle bit of oxygen, but is just a 5 % of the gas filter). 

I do not owe a Helium Conservation Module installed. We do not use either a sleep/wake mode, we just upload a different acquisition method when the sequence is completed, which runs a very low flow of helium to the system, but is never zero (0,5 mL/min). 

The Gas Clean filter was installed by a professional, so it should be fine. Nevertheless, I will try to pressurize/depressurize to remove residual/trapped air. 

Thanks for your help. 

It is important to have sufficient flow in the inlet and column to ensure that no air, no oxygen, can enter the system which will damage the column.  Lowering the column flow is fine, but the inlet needs 20ml/min of split flow.  In gas terms that is very low flow out of the split vent and septum purge to reduce back-diffusion of air.

Installing the Gas Clean filters without doing the pressurize/depressurize requires quite a lot of purging with helium to remove the nitrogen.  10 to 20 minutes at 400 ml/min.  Without serious purging and/or pressurizing/depressurizing the nitrogen can take up to some weeks to disappear.  

It's important to note that this is not trapped air....just nitrogen.  Nitrogen in the ion source reduces the sensitivity quite dramatically.

Hello Paul, 

yes! in the inlet we mantain a 20 mL/min fo split flow, it was 0,5 mL/min in the column which I meant. 

On the other hand, when we installed the Gas Clean filter, we purged a long time, using high flows (700 mL/min, split 500:1). Nevertheless, throughout the last weeks we purged it several times (within enough time), but the nitrogen wouldn't dissappear. I'll be doing more purges, to see if definetily it was nitrogen in the filter. 

Thanks, regards. 

Nitrogen contamination in gas cylinders happens frequently.  Try a different cylinder. If you're in a lab with house plumbed helium you may have to move and plumb a single cylinder immediately next to the instrument to figure it out.

If the N2:02 ratio is not approximately 4:1 or so, it is not air.

Air is: