Chromatography Forum

I've switched to a hydrogen generator, and the process has me wondering about the best style of rough pump. Currently, I run an Edwards E2M2 behind a diffusion pump on a 5971. I get 1x10-5 or a bit better using helium, but no better than 3x10-5 with hydrogen, even when reducing flow rates.

I have an old Welch belt driven 1402, and it occurred to me that a larger displacement, slower turning vane pump like the Welch might produce less oil heating and therefore better ultimate vacuum than the faster turning direct drive pumps. Does anyone have any experience comparing the two styles of pumps?

If you are running a diff pump with hydrogen that may be all the better you can hope for.

The best rough pump would be the E2M2, because those would most likely have the best ultimate vacuum for the purpose. For hydrogen the diffusion pump will give better high vacuum pumping capacity than a turbo pump would so that makes the 5971 a good instrument for hydrogen use. One thing to consider is that the ion gauge on the 5971 is calibrated for nitrogen, usually says it right on the gauge controller. Each gas will read differently on the gauge so even though it will read much higher when using hydrogen than helium you are still getting similar pressures in the vacuum chamber.

I tried hydrogen about 15 years ago on a 5971 and had the same experience, that is when I learned about the difference in ion gauge readings from the Agilent engineers. As long as you are not trying to pass a BFB tune check it will work great. The only problem using hydrogen for things like EPA 524 or 8260 is getting the m/z 95/96 ratio to pass, hydrogen likes to react with it and make the ratio too high unless you have something like a 0.2ml/min column flow rate, which is nearly impossible to control since the head pressure would be near zero.