Hi everybody,
Thanks for the prompt and numerous replies! The consensus seems to be
that normal grade 6
helium is good enough. Only one respondent thought that MR grade was
necessary, and many
hadn't tried it or even heard about it.
Astonishingly (to me), two people said they used grade 5! I was led to
believe that attaching
grade five to the cryoplatform would cause it to change lanes without
signalling, fishtail, crash
into the magnet, and ignite, taking my whole lab with it. (The details
might not be exactly
right, but it was something like that.)
Just to answer one of the respondents and give a little more detail
about the MR grade helium:
Walter Osgood at Bruker told me that he convinced Praxair to make this
product. So as far as
I understand, it was designed specifically for use with cryoprobes.
Walter tells me that if you
put grade 6 helium into a normal cylinder, the helium gets contaminated
by outgassing from
the walls of the cylinder, and often you're left with something closer
to grade 5 helium. The
reason the MR grade is supposedly better is that they use better tanks,
and they bake the tanks
to remove impurities that might outgas into the helium. And then the gas
is tested after it's put
into the cylinder to verify that it's still grade 6.
However, from my own experience and your comments I'm less and less
convinced that it's
really necessary. I'm going to think about it some more, but I may go
back to using normal
grade 6.
Thanks again!
-Robert
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Robert, We were using the regular "six nines" all the time at Kansas on
two cryoprobes, and never had any problems with it. At the time I think
that was costing us about $300 a tank.
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I've been using "UHP" helium for our cold probes. It is marked 5.0 when
there is a number on it. ca. $230 for a normal-sized cylinder. I've
never had an issue. Our 500 MHz cold probe has been running for almost 3
years (periodic warmups and cool downs for various reasons, but I've
only had the RT probe in for a few months during that time) since the
last time it was serviced and I don't have any degradation of
performance. So my opinion would be that even at $700 per cylinder
you've been spending much more than you need to. Up to now our helium
has come from MEGS (not sure what their QC is on it), but the university
contract with them has run out, and in future I'll be getting it from
Praxair- I'm assuming I'll have similar grade and similar price from them.
****************************************************************
At my old institution, we ran our Varian cold probe with 5-nines He just fine (per Varian's recommendation), and today we run our Bruker cryoprobe with 6-nines. We've never used individually-tested cylinders.
One difference between vendors is that our Varian cold probe occasionally needed "conditioning" if it was idle for a day or so. According to them, material builds up on the coil, so you run a procedure with a lot of high-power pulsing for a half hour or hour to volatilize that stuff. We've never done anything like that on our Bruker probe, and I have to wonder whether it has something to do with the grade of helium.
Regular 6-nines should still be good enough, though.
****************************************************************
Seems like a scam to me, but Bruker
sure seems to think it's necessary.
FYI, I have only used 6 9's He with
our cryosystem (at Bruker's insistence).
I'd love to hear the responses you get on this topic.
****************************************************************
Our local Praxair sells us HE 6.0RS-T for $317/cylinder. I do not have
any long-term experience with this yet, but the Bruker installation
engineers had no problems with it when we supplied it for them.
****************************************************************
Every gas supplier should be able to provide 6.0 helium, so if you can check with other suppliers besides Praxair, it might be worth it. Our 6-9's helium has a bulk certificate, and have had no problems. We have used Linde and Airgas in the past... most of the problem is delivery time, so we always have a 'spare tank' on hand, and order from the chepest supplier with certified gas.
That is very pricy gas!
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The amount of contamination specified for each of the Grade 6 gases is the same, so we use the cheaper "Electronics Grade" 6. As you say, each batch is tested. If you believe that all cylinders from one batch came out of the same tank, and you believe in the laws of Physics, then that should be good enough.
The MR grade is only for when absolute certification is required under strict ISO quality control standards. If you don't have an ISO standard that requires MR grade, you're wasting your money using it, IMO.
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Actually, I understand your concern, but from our point of view it is worth having the certificate. Bruker thinks so too. One contaminated cryoprobe system can cost easily $30K to repair and Bruker has had to deal with this at several places. Given that each of these cryoprobe helium cylinders typically last at least 1 year, it seems a small price to pay.
****************************************************************
We have been usung Grade regular 6 for years with no issues.
Presently running 9 cryo platforms.
****************************************************************
I've also used both individually-tested cylinders as well as
batch-tested cylinders, and never had an issue with it either way.
Either the "research grade" helium, whose O2 and N2 impurities are
supposed to be less than 0.1 ppm, or the "chromatographic grade" helium,
whose O2 and N2 impurities are supposed to be less than 0.5 ppm (total
impurity not to exceed 1.0 ppm), worked just fine for our cryoprobe, on
our 600 MHz system.
While I'd certainly be happier having only research grade helium
(individually tested tanks), I wouldn't be uncomfortable at all using
the batch-tested chromatographic grades of helium, since both are still
99.9999% pure.
If I recall correctly, there was some fellow even using VLSI grade (also
99.9999) helium supplied by Scott Specialty Gases, which had a guarantee
of less than 1.0 ppm for each N2 and O2, which is twice the accepted
contamination of the chromatographic grade helium that I've used a few
times.
I've also encountered a couple of folks who didn't do a good enough job
of purging the system when switching out tanks, and despite the
contamination, were still doing just fine. I suspect it's not a mistake
that they'd want to repeat, though.
****************************************************************
Just a data point for you - I've been using regular grade 6 helium with our
cryoprobes since installation in early 2007, and haven't had any problems.
Perhaps more telling, Bruker seems fine with that.
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-------- Original Message --------
Subject: AMMRL: grade 6 helium for cryoprobes
Date: Thu, 06 Oct 2011 16:59:24 -0700
From: Robert Peterson <peterson_at_mbi.ucla.edu>
To: ammrl_at_ammrl.org
Hi everybody,
I'm looking for information about "MR grade" helium from Praxair (part#
HE6.0MR-T). The difference between normal grade 6 and MR grade 6 helium
is that normal grade 6 helium is batch-tested and then put into the
cylinders, while each cylinder of MR grade is tested for purity after
it's put into the cylinders. Each cylinder comes with a certificate
showing that the helium coming out of THAT cylinder really is grade 6.
I've mostly used MR grade for the last few years, but I've occasionally
gotten a normal grade 6 cylinder and used it. I've never noticed any
difference in the performance of the cryoprobe (or any purity issues
like the preamp heater power dropping quicker). I just called them to
order a cylinder and discovered that they've approximately doubled the
price. They're now charging $1429.09 for one cylinder. At that price I'm
wondering if it's really worth it.
Does anyone have any strong opinions about this?
thanks,
-Robert
--
-----------------------------------------------
Robert Peterson, Ph.D.
Facility Manager - NMR Technology Center
UCLA-DOE Institute for Genomics and Proteomics
UCLA Dept. of Chemistry and Biochemistry
phone: (310)825-1816
fax: (310)825-0982
peterson_at_mbi.ucla.edu
-----------------------------------------------
--
-----------------------------------------------
Robert Peterson, Ph.D.
Facility Manager - NMR Technology Center
UCLA-DOE Institute for Genomics and Proteomics
UCLA Dept. of Chemistry and Biochemistry
phone: (310)825-1816
fax: (310)825-0982
peterson_at_mbi.ucla.edu
-----------------------------------------------
Received on Fri Oct 07 2011 - 13:36:51 MST