Bruker BioSpin Solid State NMR, User Manual

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CRAMPS 1D
User Manual Version 002 BRUKER BIOSPIN 279 (327)
Setup 22.4
At frequencies of 400 MHz and higher, double or triple resonance CP-MAS
probes may be used on the proton channel, at lower fields a CRAMPS probe is re-
quired due to the increased ring down time at lower field. Spinner diameters of
4mm or smaller are preferred, since we want to spin over 10 kHz. Since only one
nucleus is observed, no filters are required and should be avoided. Good imped-
ance matching between probe and transmitter is important in order to optimise the
effect of the pulses on the spins. If the RF cable has been too strongly bent or the
connectors been twisted, the cable may not have 50 Ohms and the result will al-
ways be bad. Likewise, if the preamp is burnt, it is not possible to get good results.
The fewer connectors are between probe and preamp, the better you can expect
the 50 Ohm match to be. In
edasp
, set F1 for
1
H-observation, select the high
power proton amplifier and high power preamplifier. Tune and match as usual. It
is assumed that the magic angle is precisely set, which can easily be achieved
with KBr on a double resonance probe, or on BaClO
3
*H
2
O, looking at the proton
signal, much like one does on the Br
79
resonance.
Shimming will also be important, since protons are observed, and on some sam-
ples, good resolution is expected. Looking at the protons in adamantane, find the
power level for a 2.5 µsec 90
o
pulse. Set the B
0
-field or
o1
to be close to reso-
nance (see chapter Basic Setup Procedures for more details). Calibrate the ada-
mantane proton shift to 1.2 ppm. Then load a spinner with
α -glycine (precipitate
from cold water with acetone and dry, if you are not sure about the composition of
your sample). A spinner with 50 µl or less sample volume is preferred since high
H
1
-homogeneity is desired, although it is by far less important than is commonly
stated in the literature.
Parameter Settings for PMLG and DUMBO 22.5
Table 22.2. PMLG Analog Mode
Parameter Value Comment
pulprog wpmlga Runs on AV 3 instruments only.
pl12
sp1 for 100 kHz RF field
dto, set cnst20=100 000
To be optimized during setup.
spnam1 wpmlg1, m5m or m5p
p1 2.5 µsec As for 100 kHz RF field.
p8 1.2µsec
p14 0.7 µsec To be optimized.
cnst25 140 To be optimized.
p9 4 – 2.6 µsec To be optimized.
p5 1.5 µsec or calculated from cnst20 To be optimized.
d1 4s For α -glycine.