Time requirement: 5 min Sample: Fill a solid-state rotor with finely powdered glycine.

Load standard '"*C NMR parameters. Spin the sample at 4 kHz and first run a normal CP/MAS spectrum (see Exp. 14.4). Then load the NQS pulse sequence. You have to set:

sw: 500 ppm o1: middle of ¹³C NMR spectrum o2: middle of ¹H NMR spectrum p1: 90° ¹H decoupler pulse p2: ¹H 5 ms spin-lock decoupler pulse p3: ¹³C 5 ms spin-lock transmitter pulse p4: 180° ¹³C transmitter pulse d1:3s decoupler attenuation for cross-polarization decoupler attenuation for high-power cw decoupling, typically 2 dB less than for cross-polarization; on instruments with no fast power switching use same attenuation as for cross-polarization rg: receiver gain for correct ADC input de: as short as possible

5. Processing

Use standard 1D processing for ¹³C NMR as described in Experiment 3.2 with zero- filling to 4k and exponential multiplication corresponding to the line-width using lb =

6. Result

The figure shows the spectra of glycine obtained using a multinuclear solid-state probe-head with a 7 mm rotor on an AM-400 spectrometer with wide-bore magnet. The spinning rate was 4000 Hz as seen from the standard CP/MAS spectrum in a, whereas in b the result of the NQS sequence is given.

7. Comments

The sequence is similar to the standard CP/MAS procedure with the difference that before the acquisition the decoupler is switched off for a very short time, typically 50 vs. During this time protonated ¹³C nuclei will feel the dipolar coupling and dephase rapidly. A 180° ¹³C pulse refocuses chemical shift evolution during this time and thus