Dear isotopers,

in early November Linde informed us about problems
concerning the general availability of helium. Today the
anouncement turned into reality and our local Linde gas
supplier declared that He 5.0 currently is not available.
The highest available quality is 4.6.

Quite a number of years ago we ran into considerable trouble
using He 4.6 for (GC/C/)IRMS (linearity, precision, ...).  
Consequently we switched to 5.0 and additionally we mounted
Supelco "High Capacity Gas Purifiers" (Supelco 23801).  
According to the Supleco catalog these however remove H20,
O2, CO2, and CO, but nothing is specified concerning other
contaminants. Of course we didn't systematically investigate
the effects of different He purities and the purifier! We
just were happy that analytical accuracy & precision were 
back after a bothersome while.


Now here come my questions:

  1) Does anybody have experience with the combination of He
     4.6 and the Supelco gas purifiers? Is the achieved 
     purity sufficient for IRMS?

  2) Does anybody have experience with gas purifiers that 
     work on a larger scale? More specific: Is it possible 
     to use He 4.6 in combination with a powerful gas 
     purifier and supply ca. 10 machines (not only IRMS's!)
     at justifiable expense?

  3) Not only for academical reasons: What is the nature of 
     the contaminants in Helium? When we had the 
     abovementioned problems, no signifcant contaminants 
     could be identified in the He 4.6 as judged from the 
     mass spectra. (We connected the tank to an Agilent MSD 
     5973.)

  4) How can the quality of the Helium be monitored 
     efficiently? I know there are small quads, that can be 
     connected to the gas line or the vacuum system. But are
     these suited to find the contamination relevant in 
     IRMS? Which contamination is relevant at all and causes 
     e .g. "non-linearities"?


A lot of stuff, admittedly. But if I read the Linde message
right, these are pushing questions and I feel they concern
the whole IRMS community and even a lot more analysts
working in other fields. I also don't think that only Linde
customers are affected. As far as I know there is only a
restricted number of He sources which represent the 
fundament for many suppliers. 


I'm looking forward to your comments. 

Many greetings from Cologne ...

-- 
	Uli Flenker

	Institute of Biochemistry
	German Sport University Cologne
	Carl-Diem-Weg 6
	50933 Cologne

	+49(0)221/4982-5060