4. Acquisition

Time requirement: 20 min Sample: 3% strychnine in CDCl₃ Prior to the experiment the 90° pulse-width and transmitter attenuation for the spin-lock pulses must be calibrated (see Exp. 2.9). For optimum results on older instruments one should make allowance for the phase difference between the hard pulse p1 and the spin-lock pulses, either in the pulse program or in the adjustable parameter set if the software allows (see Exp. 7.1). Run a normal ¹H NMR spectrum of the sample and optimize the spectral width. Load the TOCSY program; the duration of the spin-lock is an adjustable parameter. You have to set:

td2: 1 k data points in F, td1: 128 data points in F; sw2: 10 ppm sw!: 10 ppm o1: middle of ¹H NMR spectrum p1: 90° ¹H transmitter pulse p2: 'Htrim pulse, 2.5 ms at transmitter attenuation of spin-lock [12 dB] p3: series of composite 180° ¹H pulses (90°, 180°, 90°) at transmitter attenua- tion of spin-lock; 90° pulse-width and transmitter attenuation typically in the order of 40 μs and 12 dB, corresponding to an effective spin-lock field of ca. 7000 Hz (magnetic field dependent). Total length of spin-lock set to 200 ms by loop parameter of spin-lock sequence. The loop parameter must be an even number; 76 was used here. d1:2s initial value for f; evolution: 3 μs increment for f, evolution: 1/[2-sw1] ds: 2 ns: 4

5. Processing

Apply zero-filling in F' to 512 real data points to obtain a symmetrical matrix of 512 512 real data points. Use exponential windows in both dimensions corresponding to