Varian Solid-State NMR - Page 24

2.4 Spinning the Sample
01-999162-00 C0402 VNMR 6.1C User Guide: Solid-State NMR 24
Spinning Rates and Adjusting Bearing and Drive Pressures
Spin rates and the bearing and drive pressures for the Varian CP/MAS probe at ambient
temperature are listed in Table 3 for the 7-mm probe and Table 4 for the 5-mm probe.
For 5-mm CP/MAS probes, spinning a sample with a small amount of drive gas before
applying the initial 28 psig (2.0 bar) of bearing pressure is sometimes useful. The rotor will
begin spinning and will therefore become less likely to flutter (slight motion in and out of
the stator) during initial spin up.
To avoid rotor explosions, never spin 7-mm zirconia rotors faster than 7200 Hz and never
spin 5-mm zirconia rotors in Varian probes. Also, never spin 7-mm silicon nitride rotors
faster than 9500 Hz or 5-mm silicon nitride rotors faster than 15000 Hz.
Overcoming Imbalance
Most of the spinning problems encountered with filled rotors result from imbalance caused
by the sample material. A damaged rotor might be at fault, but that can be eliminated by
Table 3. Typical 7-mm CP/MAS Probe Spin Rates With Bearing and Drive Values
*
Rates are approximate values for the Varian 7-mm CP/MAS probe at ambient temperature.
The actual spin rate will vary depending on the properties of the sample and sample holder.
Spinning Speed*
(Hz ±250 Hz)
Bearing Drive
Pressure
psig (bar)
Flowrate
(LPM ±2
LPM)
Pressure
psig (bar)
Flowrate
(LPM ±2
LPM)
2500 28 (2.0) 12.5 7 (0.5) 15.0
4000 28 (2.0) 12.5 14 (1.0) 20.0
5000 36 (2.5) 12.5 21 (1.5) 25.0
6000 36 (2.5) 12.5 28 (2.0) 27.5
7200 36 (2.5) 12.5 36 (2.5) 30.0
8000 44 (3.0) 10.0 51 (3.5) 35.0
8500 44 (3.0) 10.0 58 (4.0) 37.5
9000 44 (3.0) 9.0 65 (4.5) 40.0
Table 4. Typical 5-mm CP/MAS Probe Spin Rates With Bearing and Drive Values
* Rates are approximate values for the Varian 5-mm CP/MAS probe at ambient temperature.
The actual spin rate will vary depending on the properties of the sample and sample holder
Spinning Speed *
(Hz ±250 Hz)
Bearing Drive
Pressure
psig (bar)
Flowrate
(LPM ±2 LPM)
Pressure
psig (bar)
Flowrate
(LPM ±2 LPM)
4500 28 (2.0) 12.5 7 (0.5) 15.0
7000 28 (2.0) 12.5 14 (1.0) 20.0
11500 49 (3.5) 12.5 35 (2.5) 25.0
13000 56 (4.0) 9.0 63 (4.5) 40.0