Chromatography Forum

For reference I am using a 7890a Agilent GC, a 5975c Agilent MS, and a 7697a Agilent Headspace Auto sampler.

I have been picking up a huge response for m/z 40 during my air and water check but only when I am connected to the inlet of my GC and thus the carrier gas (I have a transfer line hookup). When I cap the column off and let the mass spec pump down for an hour or two I have no leaks and no m/z 40.

As soon as I connect the column to the inlet I get the 40 back but no leaks. Water, oxygen, and nitrogen are all lower than 5% and after 24hrs less than that.

I have notified my gas supplier as I suspected argon contaminated helium, and they sent me two new cylinders. I hooked up one and I am still getting this strange 40 response.

Other than it being contaminated helium, what else could be causing this?

Thank you.
Wendy

I fear that you have a few contaminated tanks. I had this happen a while back but I was fortunate that the next tank I chose didn't show that contamination. Where I first saw it was in my HID (very high background). I then tuned a mass spec and sure enough, m/z = 40 dominated the tune.

My gas supplier [Weldstar/Purity Plus] had some issues with cylinder mix ups and gross contamination with argon and in one case nitrogen when they switched to new labelling for the global harmonized SDS. It is probably your cylinder.

The issue is resolved!

It turns out several of the helium tanks had argon contamination or quite possibly; a helium tank was filled with argon. The argon saturated my filter system and once I bypassed the filter, with a new tank of helium, I no longer have the hit for 40.


Thanks so much for your advice!

Excellent! I'm glad you figured it out.