td2: 1 k data points in F, tdl: 128 data points in F, sw2: 8 ppm sw1: 40 Hz (width of largest multiplet) o1: middle of ¹H NMR spectrum p1: 90° ¹H transmitter pulse p2: 180° ¹H transmitter pulse dl:2s initial value for ¢; evolution: 3 μs increment for ¢, evolution: 1/[2-sw1] pre-acquisition delay: as small as possible

5. Processing

Apply zero-filling in F, to 256 real data points. Use unshifted sinusoidal windows in both dimensions. Apply complex Fourier transformation corresponding to the N-type signal selection using the quadrature-off mode in F). Phase correction is not necessary, since the data are processed in magnitude mode. After the Fourier transformation the spectrum is tilted, since the signals are also modulated by J in F . This tilt can be eliminated by a software command. Finally the data may be symmetrized with respect to the horizontal through the center of F;.

6. Result

The figure shows the 2D spectrum obtained on an ARX-200 spectrometer after the tilt and symmetrization operations. The high-resolution spectrum is shown on the F; axis; the internal projection (not shown) would give the ¹H-decoupled proton spectrum. In F, the individual proton multiplets are observed.

7. Comments

The sequence is, in principle, identical to that in the spin-echo technique as described in Experiment 6.2, but differs in that the spin-echo delay is now incremented, with T= ft, thus creating the second dimension. At the end of #, the chemical shift information is refocused. However, the echo is modulated by the spin-spin coupling that evolved during f,, and thus a 2D Fourier transformation will separate these two signal components. Well-resolved multiplets are obtained in F,, because line broadening due to field inhomogeneity is refocused. Artefacts due to higher-order spin systems may occur [4]. There also exist selective and doubly-selective variants of this technique, see Experiment 7.11. The 2D spectrum cannot be recorded in the phase-sensitive mode