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- Posts: 355
- Joined: Mon Jul 30, 2018 11:58 pm
- Location: Louisville, KY
The GC-MSs go through periods of heavy use, and then at times might not get used for a couple of weeks at a time, or maybe get 1 sample a day and then go back to idle. Both of them(one a 5890/5971, the other a 7820/5975) are set up with a "rest" method that flows .5mL/min He and switches to splitless mode when not being used. Still, though, they can go through a fair bit of He when not being used(I'm at about 4 months on a cylinder, when I'd like 6-8 months).
Not too long ago, I was reading about the 8890/5977, and one of the features mentioned was the ability to switch to a less expensive gas when resting.
That got me to thinking that it might be possible to do something like that in my set-up. In my mind, it should be possible to put a selector valve on the carrier gas line leading to the GC-MSs, and then just plumb He to one side and N2 to the other side. Since loading a new method(our instruments are used by several different research groups and for several different projects, so we have probably over 100 different methods on them) usually takes several minutes for the temperatures to equilibrate, that would also give time to flush all of the N2 out of the lines and switch over entirely to He.
I haven't checked on the prices of UHP/Zero Grade N2, but I know I pay about $10 for the cheap stuff, and I'm sure UHP or Zero has to be less expensive than the $200+ I'm paying for zero grade He.
The long term plan is to switch over to H2 for the GC-MSs, but I have too many PhDs in progress to get away with that now. So, in the interim, does anyone have any thoughts on the above plan?