Hi, a sample broke in (or on the way into) our 500 MHz HCN probe. There was sample and glass on the top of the probe, and a small piece of glass stuck right at the top of the insert. To the best we could see with a flashlight, and gently cleaning with a qtip, it did not seem like contamination went very far. The probe, upper barrel, sample changer and depth gauge all got thoroughly cleaned, and we put the probe back in. I say the probe was thoroughly cleaned: all the dirt on the flat service and at the very top cm or so was well cleaned gently with methanol on a qtip, and I gently wiped the sides going a bit further down.
Protune failed, and at first I thought it was an indexing issue... but after disconnecting protune, checking the tuning manually, and verifying the range of motion of the tuning rod, it seems that we can no longer tune to the correct frequency, even if the tuning rod moves smoothly through the normal number of turns (11, same as another hcn probe). The gradient profile looks nice, and the shims seem fine (although weak signal due to poor tuning in a single scan line-shape experiment-). 13C and 15N tune just fine. I didn't check 2H tuning, but given the S/N in the gradient profile I have no reason to suspect it is out of tune.
There is a very nicely matched dip at ~496 MHz, and it moves a little closer to tuned (which would be 499.8) when there is no sample in the probe. This is at the highest frequency end of the tuning rod range. Prior to the broken sample issue all was in working order, to the best of our knowledge.
Any ideas as to what to check, in-house fixes (we have a great electronics shop) or is our favourite probe on its way out for repair?
Thanks,
Tara
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Dr. Tara Sprules
QANUC
Quebec/Eastern Canada High Field NMR Facility
www.nmrlab.mcgill.ca
phone: (514) 398-1721
fax: (514) 398-8254
3420 University St., Rm 023
McGill University
Montreal, QC, H3A 2A7
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Received on Mon Nov 04 2019 - 10:55:27 MST