I have been having a problem lately with NMR tubes breaking in the
probe. I have not witnessed the phenomenon myself, but it has happened
now to 3 different users on 4 separate occasions. The occurrences are
sporadic and go like this; a user inserts their sample but has trouble
shimming. Upon ejecting their sample they find the tube is broken. The
user then gets me. I drop the probe and find the tube is broken at the
top of the probe. I dump out their sample and tube (which is intact
below the break). I clean the probe with Ethanol, reinsert it, and
continue with routine use.
The system is a Varian 300 "R2D2" style magnet. It has been in use for
many years and has not demonstrated this behavior before. No changes
were made to the system around the time the problems started.
The problem does not seem to be tube related. All users use the same
tubes and in at least one case the tube was brand new.
The problem does not seem to be bearing related. After the first
instance I "retired" the bearing, yet the problem persists.
My suspicion is that the problem is related to the air supply. Either
the slow drop or the spin air. I don't think it is the slow drop air
because a problem there would likely cause the tube to shatter or break
at the edge of the bearing, not at the edge of the probe. My best guess
is that when the sample is beginning to spin it oscillates causing it to
break at the top of the probe.
Any suggestions on how to trouble shoot this problem? Any other
plausible scenarios?
I'll summarize the replies and re-post at an appropriate time.
Thanks.
Nathan Dubree
Genentech Inc.
Received on Wed Nov 29 2000 - 13:17:50 MST