Thanks for all the advice and offers of help:
We checked the probe tuning again a couple of days after the initial problem before taking any further action. It had improved, although was still not covering the normal range. As the gradient profile looked very much like normal, and gradient shimming had converged quickly as usual, we decided that the most likely (and easiest to address) problem was contamination from the broken sample. So we inverted the probe, and gently squeezed methanol, followed by isopropanol through the VT inlet. We then flushed with nitrogen gas for several hours, and left it upside down in a quiet corner over the weekend. This morning the whole tuning range was back, and the probe is back in the magnet working just fine, with better lineshape than we have had in a while.
We left the Protune driver module turned on the whole time, although we'd switched to a non-Protune probe while our usual one was out of commission. I manually tuned on the lineshape sample before attaching the motor cables. The tune and match for standard solvents only use a relatively small range of the total capacity, so it was nice to see that upon indexing, there was a small correction made to the displayed positions, and subsequent samples that I checked all tuned and matched easily.
We did take the cover off the probe to verify that there was no obvious problem with the tuning rod (the probe is long past warranty, and we've removed probe covers in the past so were confident we could do so without mishap), but given the same symptoms again, I'd leave off this step and go straight to rinsing well and extensive drying.
Great resource, as always,
Tara
*********************************************
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
*********************************************
________________________________
From: Tara Sprules, Dr. <tara.sprules_at_mcgill.ca>
Sent: Monday, November 4, 2019 3:55 PM
To: ammrl_at_ammrl.org <ammrl_at_ammrl.org>
Subject: AMMRL: tuning issue after broken sample
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
*********************************************
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
*********************************************
Received on Mon Nov 11 2019 - 18:21:34 MST