We use Edwards scroll pumps to back the turbos on our organic 
electrospray instruments and they work OK at a much higher pressure 
(1-2mBar) than those routinely pumping analysers including stable isotope.
The advantage of scroll pumps is that you no longer have the problem of 
oil backstreaming back up the line to the turbo and causing possible 
The disadvantage is that you have to change the scroll seals every 12-18 
months or so and this is fiddly job and the seals I bought this year 
cost 225 GB PDS each from Edwards.

John Hill
Mass Spectrometry Facility
University College London

Chris Yarnes wrote:
>  >From a quick search of the Archives, it appears others on the list 
> have wondered about the utility of scroll pumps over rotary pumps on 
> IRMS systems. 
> For those of you who have wondered, have any of you tried using scroll 
> pumps to back a turbo?
> If so, I'd be interested in hearing about your experience(s).
> Thanks,
> Chris
> -- 
> Chris Yarnes
> Stable Isotope Facility
> Department of Plant Sciences
> Univ. of California-Davis
> One Shields Ave.
> Davis, Calif. 95616
> 530-752-8100