Fingers crossed - I think I have the answer from the kind spinlanders who
are not on vacation (I received a lot of "out of the office"
robo-relies)..very envious of those who are away. Having done NMR for 30+
years I have to say that this was a first and I learned something new today.
Thanks to Dr Bert Heise, Dimitri Argyropoulos, and Letitia Yao and Ryan
McKay for the rapid suggestions.
Here is the reply from Bert Heise that cracked the case (and Dimitri also
nailed it).
"Did you possibly just do a helium filling or had a considerable change in
weather/air pressure? These artifacts could come from wave ripples in the
helium bath. Remedy if you don't want to wait (should reduce after a while):
open briefly (few seconds) one of the helium turret plugs to let off a bit
of "steam". Check again.
Another source of similar problems could be a failing capacitor in a power
supply but that should result in 50/60 Hz spikes..."
I indeed have a full helium bath (filled yesterday with the now precious
liquid) and the boil-off was noticed to be quite high this morning perhaps
due to a weather front. I popped the helium can pressure valve and ran the
sample that was giving me problems again - no 27 Hz artifacts this time.
Helium boiloff had dropped from 12-16 to about 6 cc/hr. I didn't know that
such a phenomenon existed.
I love this group. Hopefully we can all keep our magnets running!
John
John C. Edwards, Ph.D.
Principal - Process NMR Associates, LLC
84 Patrick Lane, Ste 115, Poughkeepsie, NY 12603
Tel: (845) 240-1177, Mobile: (203) 241-0143
From: John Edwards <john_at_process-nmr.com>
Sent: Thursday, June 27, 2019 1:56 PM
To: 'ammrl_at_ammrl.org' <ammrl_at_ammrl.org>
Subject: 27 Hz artifact peaks in Varian Mercury 300 1H NMR spectra
Greetings,
I have suddenly developed a problem with 27 Hz artifact peaks that appear
around each peak in a 1H NMR spectrum (very ugly on the most intense peaks
but proportionately also present around the TMS peak - they seem to be
pretty much anti-phase - they do not signal-average away and often get
bigger when you reach the magic multiples of 16 on the co-averaging. They
are present spinning and non-spinning and also present when the sample is
run unlocked. They are about the same size as the 13C satellites. Other than
these artifacts cycling through the spectrum everything seems fine - shim
and sensitivity are good.
The system is a Varian Mercury-MVX300, with a 5mm ATB probe with PFG,
running VNMRJ 4.2
Not sure if the same artifacts show up in 31P or 13C spectra - will know
soon.
Thanks for any help,
John
John C. Edwards, Ph.D.
Principal - Process NMR Associates, LLC
84 Patrick Lane, Ste 115, Poughkeepsie, NY 12603
Tel: (845) 240-1177, Mobile: (203) 241-0143
Received on Thu Jun 27 2019 - 11:34:05 MST