According to our gas supplier, many of the different grades of helium are often from the same giant tank and contain the same helium, but many cylinders aren't labeled as the higher grades simply because they haven't been verified to be a higher grade. 
In other words, a cylinder labeled as a lower grade could be that grade or higher and just hasn't been tested, but a cylinder labeled as a higher grade has actually been tested and found to be of that grade. I don't know if this practice is common for most suppliers or where along the supply chain those tests for grade are undertaken.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
University of Arkansas Stable Isotope Laboratory
http://www.uark.edu/ua/isotope/
http://comp.uark.edu/~tmillic


----- Original Message -----
From: Matheus Carvalho <[log in to unmask]>
Date: Thursday, October 25, 2007 4:35 am
Subject: Re: [ISOGEOCHEM] why He is in short supply
To: [log in to unmask]

> I will give only a personal view here. If the problem
> is mor with purity, then it might not be a so big
> problem, sometimes. For example, in the past in our
> lab we mistakenly connected He for baloon in the gas
> bench and ran some samples. The results were fine for
> d13C and dD. By "fine" I mean that repeated samples
> showed consistent results. We didn't scrutinize these
> results in deep to see if any bias existed, but for
> our purposes no big effect was felt.
> 
> 
> --- Ulrich Flenker <[log in to unmask]>
> escreveu:
> 
> > Dear Colleagues,
> > 
> > apart from technical progress, that will hopefully
> > help us
> > to save or recycle He in the future, it would also
> > be of
> > interest what can be done now, to cope with the
> > situation.
> > Not long ago we ran into problems to purchase He of
> > sufficient purity to maintain our routine work. I
> > talked to
> > several vendors then, and all of them told me, that
> > not the
> > availability of He itself represented the problem,
> > but
> > rather the required purity.
> > 
> > So, does anybody know a way to purify technical He
> > to
> > qualities of 5.0 or 6.0 at the laboratory scale? For
> > the
> > time being this would at least help lowering the
> > costs.  
> > We're using SUPELCO purifiers in front of each
> > machine
> > anyway, but I don't think these devices are able to
> > sufficiently purify, say He 4.0 or 4.5.
> > 
> > BTW, has anybody considered to return to good old
> > hydrogen 
> > for the "ordinary" GC work?
> > 
> > Best ...
> > 
> > -- 
> > 	Uli Flenker
> > 
> > 	Institute of Biochemistry
> > 	German Sport University Cologne
> > 	Carl-Diem-Weg 6
> > 	50933 Cologne
> > 
> > 	+49(0)221/4982-5060
> > 
> 
> 
> Matheus C. Carvalho
> PhD student
> Kitasato University - School of Fishery Sciences
> Japan
> 
> 
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