I recently posted a general question about purchasing 3rd party used
probes. Here are the responses I got. One of the main feedback questions
concerned the state of the 4 nucleus probe I am having trouble with.
It's a first generation 4 nuc probe (c. 1993) and it has always been a
beast to shim . I hear from reliable sources that the first generation
probes have a reputation for this. These days time is of the essence and
spending 30 minutes shimming every time I switch probes in and out to
get a single 1H spectrum is getting old quick, especially as I'm a
solids guy who hates shimming. Thanks to everyone.
John C. Edwards, Ph.D.
Manager, Process and Analytical NMR Services,
Process NMR Associates, LLC
87A Sand Pit Rd,
Danbury, CT 06810, U.S.A.
Tel: +1 (203) 744-5905
Mobile: +1 (203) 241-0143
Fax: +1 (203) 743-9297
e-mail: <mailto:john_at_process-nmr.com> john_at_process-nmr.com
web: http://www.process-nmr.com
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We have purchased several probes from Nalorac over the last several
years for our Varian INOVA 500 & 600 systems. They have all been quite
good are shim easily to give excellent lineshape & sensitivity. Of
course, Nalorac is not really "third party" anymore, since last winter.
What make/vintage is the four nucleus probe that you have trouble
shimming? If it's an older model, you might want to investigate having
it update with the newer balanced-susceptitiblity coils with shielded
leads.
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That probe should shim just fine unless it has a cracked quartz insert (or
unless it is old and is constructed from materials with poor magnetic
susceptibility matching). Bruker or Varian?
To answer your original question, I think the 3rd party vendors are fine
for buying used probes, as long as they are not custom made probes
(i.e., not made by Bruker or Varian or JEOL or whomever). Probes can always be
returned if they don't perform as promised, and fixes aren't that much
compared to purchase.
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Has your probe always been a problem to shim or is this a recent
event? I'm wondering if the glass insert in the probe is broken, which
can cause all sorts of problems. If you pick up a probe from
someone else, make sure it meets specs before you accept and pay
for it. You should have a specific linewidth for 1H, as well as a
decent S/N (~200 on .1%EtBz). Also, you shouldn't have any
spinning problems.
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I have purchased a probe from NMR Associates, He did a great job
installing and I would highly recommend them. Contact info is Arnold _at_
1-978-632-0312
http://www.nmr-associates.com/index.htm
By the way, We have a 600 MHz system that has quite a bit of available
time. It has CPMAS, HRMAS, TXI (1H/2H/13C/15N), and a BBO probe as well
as an autosampler. Would you be interested in utilizing this equipment?
I am allowed to do consulting work on the system.
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Just be able to fend off potential finger pointing from both sides
(instrument vs probe). In other words, be able to prove that your
instrument is working properly with another probe. When the new probe is
brought in and the engineer is shimming, etc, you don't want to get
caught in the middle if the probe does not meet spec.
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We have one 500 MHz and two 300 MHz Nalorac (now Varian) four nucleus
probes that have worked well for several years.
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We have bought a 500MHz dual BBO probe from UMinn and it
was fine...certainly most labs are going to be upfront
about problems. We paid, I think $2k for waht would have been an $8-12K
probe new...so it if needed a new capacitor with a few hours work in the
Bruker shop it would still have been fine.
I think you can be optimistic: just don't pay much ...which is pretty
standard. Used probes do not go at high prices.
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Some 4 nuc probes can be are a bear shimming. I suggest you make an
agreement with the vendor that you can keep the dual for say a week the
shims should improve with each iteration. I guaratee there is somebody
out there who would LOVE to have your 4nuc probe. We have several that
we like enough to send back for full freight factory repairs ... usually
3$K-6$K each incident. Do you know the full history of the probe? If
it was repair by an outside agent ... chances are he cut corners on
materials because most makers won't easily sell the actual part unless
you get really nasty with them. I had to do it once with Varian and
they still did not supply all the parts need to complete the repair
properly.
Bottom line. You get what you pay for and if you pay low $ for a probe
then you may need need very high-caliber shim-gods to shim it first.
Newer generation probes have exquisite trade-secret protected materials
with very special magnetic susceptibilities. Different materials change
the shape of the field where it matters for lineshape. This is why the
high $ probes regardless of maker shim up so fast and nicely.
There may also be something wrong with your probe or shimstack position
that is affecting your 4nuc's shimming. There are simple devices that
you or your engineers can make to check probe positon and shim-stack,
shim-coil, B-field correlation. You can use the water drop method
explained at the acornnmr website. I have modified this method using a
micrometer and a glass sphere of water and can detect easily differences
a low as .5 mm problems with shim-coil, magnet field alignment.
It's either time or money ... sometimes both. A rarity in either makes
makes high-end NMR a challenge. I humbly suggest that you seek
professional paid service on occasion. Take him or her to dinner and
enjoy the visit ... have a laundry list ready son they aren't standing
arround shadow and learn by mostly watching. It's worth it.
Received on Tue Dec 10 2002 - 17:35:33 MST