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Date: Wed, 26 Feb 1997 10:55:47 EST
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Hello,
We have recently received a new Avance Bruker 500, which is still in the
process of being installed. It has a self-shielded Magnex magnet.
We have run several resolution tests overnight or over the weekend, where we
collect a different spectrum at the beginning of each hour with one scan per
spectrum. We are using the dioxane/acetone-d6 line shape standard and a
controlled temperature of 27 or 30C. We see the resolution decay with time.
For example, the signal has the following width in hz at half height and at 10%
of full height as a function of time:
time width at half ht with at 10% of max ht
---- --------------- ---------------------
1 hr 0.84 3.36
16 hr 1.07 6.57
60 hr 3.51 11.14 peak is split into two at top
We see the same results locked or unlocked, with or without the drift
compensation on. If we shim up the sample and then move the field (changing
z0) and take another scan right away, the line stays shimmed up with no loss of
resolution. We are running a similar test on the 400 MHz Varian system in the
same room. So far it looks OK, but we need to do that some more to exonerate
room conditions.
I am wondering what is the norm for a 500 Mhz magnet. Should I expect this
loss of resolution with time? What could be happening?
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