Time requirement: | h Sample: 3% strychnine in CDCl₃ Record a normal ¹H NMR spectrum of the sample and optimize the spectral width.

Change to the 2D mode of the spectrometer software and load the pulse program for gs-DQF-COSY. You have to set:

td2: 2 k data points in F2 tdl: 512 data points in F; sw2: 10 ppm swl: 10 ppm o1: middle of ¹H NMR spectrum p1, p2, p4: 90° ¹H transmitter pulse p3, p5: 180° ¹H transmitter pulse d1: 2 s; often a longer repetition time (d1 still longer) reduces the antidiagonal d2: equal to effective duration of gradient used, here 2 ms initial value for ft, evolution: 3 μs increment for ¢, evolution: 1/[2-sw1] g1, g2: sinusoidal-shaped field gradients with 1% truncation, 2 ms duration and 0.1 T/m strength, with gradient loop counters, ring-down delays (100 ps), lock blanking and gradient coil blanking switches according to actual instrumentation used. Gradient strength ratio: | : 2.

rg: One must be very careful in setting the receiver gain for this experiment.

The gradient filter allows only the desired coherences to pass into the receiver; however, the double-quantum coherences develop only at higher ¢, increments. The receiver gain must therefore be set using a high ¢, increment to avoid overloading. ds: 4

5. Processing

Apply zero-filling in F, to 1 k words in order to have a symmetrical matrix of 1024 1024 data points. Use exponential or Gaussian windows in both dimensions cor- responding to the Hz/point resolution of your data set. Apply real Fourier transforma- tion in both dimensions. Phase correction in F can be performed after the 2D transformation in order to get clean up/down patterns of the cross-peaks. Zero order phase correction of 90° has to be applied in the F, dimension.

6. Result

The figure shows the expansion of a 2D spectrum obtained on an AMX-500 spec- trometer with an inverse multinuclear z-gradient probe-head and a BGU (10 A) gradi- ent unit. Note that dotted contours represent negative signals.