Bruker BioSpin Solid State NMR, User Manual

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86 (327) BRUKER BIOSPIN User Manual Version 002
Basic Setup Procedures
Remember which way to turn the tuning knob to tune to higher and lower frequen-
cies. On most probes, turning the adjustment counter clockwise tunes to higher
frequency. Do not change the matching adjustment until you have found the cur-
rent tuning position of the probe, else you may loose the probe response totally.
Do not tune without having the appropriate matching box fitted to the preamp.
Fake resonances may appear due to filters between probe and preamp, because
filters are also tuned circuits. Remove all filters before tuning over a wide range,
and fine tune again (
wbsw
≤ 10 MHz) when the probe is tuned close to the de-
sired frequency.
Changing the proton tuning will affect the X-tuning, so always tune the proton
channel first, then the X-channel.
Setting a probe from high range to low range mode (lambda/4 switch) will shift the
X-tuning to lower frequency by many MHz, the proton frequency will only change
by a few MHz.
An empty probe may tune as much as 10 MHz higher on the proton channel com-
pared to a probe with a spinner in.
When a probe has not been used over an extended period, humidity may collect
inside the turbine, causing a few harmless arcs (RF-breakthrough) on the proton
channel. If the arcing does persist and/or gets worse, have the probe checked.
Usually this means that dirt has accumulated inside the turbine or on the RF-coil.
Cleaning should be done by a trained person only.
Regular probe performance checks comprise:
•
Checking the magic angle setting (KBr)
•
Checking the shims (Adamantane)
•
Checking S/N performance on glycine
These checks must also be performed after a probe repair. Since a repair may re-
sult in a more efficient power conversion, start with slightly reduced power set-
tings.
SB probes flip the stator vertical for sample eject. These probes require some
more effort to assure a correct angle setting.
Remember to always approach the magic angle setting from the same side!
To check the reproducibility of the magic angle setting, take a KBr spectrum, stop
spinning, eject and reinsert the sample, take another spectrum into a new data
set, compare in dual display mode.
If the second spectrum is worse, dial less than 1/8
th
of a turn counterclockwise .
Take another spectrum, compare again.
A laboratory notebook should be kept with the following entries (a suitable form
for printout is supplied in the
"Appendix"
):
•
Name of the shim file and field value for every probe.
•
Value of power level in dB and power in watt (if available) for proton decou-
pling (
pl12, pl12W
) and associated pulse lengths
p3
, pcpd2 .
•
Value of proton contact power level in dB and watt (
sp0, sp0W
).
•
Value of carbon contact power level (
pl1, pl1W
) and associated pulse length
p1
.
•
S/N value obtained on glycine,
SR
value for shift calibration, line width on α -
carbon in Hz.