> I am wondering if anyone has dealt with these problems before, or has any
> advice. Given that we are only running a Gemini 200 and not a 600 or 750
> (I wish! :-) ) even if forces within the 1 gauss line do effect the magnet,
> is it likely to be noticeable on this instrument??
> What about vibrations to the instrument?
I recieved a few replies, the advice in one I am still hoping to follow up
on. I also recieved a request for replies. So here goes.
My own investigations so far have shown no difference in a standard DQCOSY
of 3-heptanone run from 8.30am-8.30 pm (with cars and trucks) and another
run from 8.30pm-8.30am (without traffic)
I also recieved verbal advice from an NMR service engineer that
manufacturer's specs on Gauss lines are notoriously conservative, in order
for the vendor to remain on the safe side of problems re stray fields.
So maybe we don't have a problem - altho my interest has been diminished
somewhat by word from above that the He fill due in 10 days will be the
last.
Many Thanks to those who replied.
Ross
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uncertainty about the traffic and its effects could be the biggest
problem. At my last position, I had a Bruker AC-300. It was on the third
floor of the Chemistry building and all the airhandling equipment was in
the attic above. I felt, although I never substantiated it, that a number
of the transient problems I had over the years could have been due to
equipment movement and motors switching on and off. So, my point is that
even if there seems to be no easily detectable effect, you will probably go
crazy and start atributing things to this unquantified outside interference
-----
Our problem related to afterhours cleaning crews
waxing the corridor floors adjacent to these instruments.
The test to measure the effect was simple: Acquire a 1H spectrum
with a D2O sample, unlocked every few seconds (pad) and move metal
around the areas of concern. Bottom line, a 22 KG floor-waxing
machine moved our 300 WB 1H line ~ 5 Hz when it was just beyond
the 5 Gauss line. Locked, we saw no affect whatsoever. The only
NMR experiments that were at risk were nOe difference and HMBC-types
with very low nt. Moving the metal mass inside of the 5 guass
line moved the line ~20 Hz, unlocked.
Our problems were ultimately found to not be related to iron
brushing our field edges. I would suggest parking a truck
near your magnet and monitoring the line-shift as we did.
Vibration is very likely to cause you problems IF you run HMBC
and/or inadequate 2D. nOe difference would also not like the
jostling.
-----
I did not see any interferenc with cars who are
placed just outside the 5 Gauss line (6.1 meter), so the field is
still 2 Gauss at the parking-place. This is not carefully checked and
also not recommended but in practic until now I dont see a lot of
effects from something moving inside the 1 Gauss and outside the
5 Gauss-line !!
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Ross Mair Email: rmair@stan.xx.swin.oz.au
NMR Lab Snail: Mail 41, Swinburne University,
Applied Chemistry Dept PO Box 218, Hawthorn, 3122.
Swinburne University of Technology Fax: +61-3-8190834
Hawthorn, Victoria, Australia Voice: +61-3-8198843
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