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Date: | Mon, 11 Dec 2006 11:49:53 +0100 |
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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
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