limited dynamic range of NMR ADCS, additional solvent suppression has to be performed before digitization (i.e, presaturation) If the dQ filtering is done with pulsed field gradients(PGFs)instead of phase cycling, then this suppresses the solvent signals before hitting the digitizer. However, inserting PGFs into the dQF-COSY sequence causes other problems(additional delays and r f. pulses, phase distortions, non-absorptive lineshapes, additional 50% reduction of S/N) With the normal COsY sequence, they result in gigantic dispersive diagonal signals obscuring most of the 2D spectrum Intensity of cross-and diagonal peaks In the basic COSY experiment, diagonal peaks develop with the cosine of the scalar coupling, while cross-peaks arise with the sine of the coupling. Theoretically, this does not make any difference(FT of a sine wave is identical to that of a cosine function, except for the phase of the signal). While this is normally true for the relatively high-frequency chemical shift modulations (up to several 1000 Hz), the modulations caused by scalar coupling are of rather low frequency(max. ca. 20 Hz for JHH), with a period often significantly shorter than the total acquision time xg1o⊥lLL Time development of in-phase(cos Tty and antiphase(cos Tty) terms, with $2/=50 HE, J=2 H, for T2=10 s(left) and T2=0. 1 s(right) While the total signal intensity accumulated over a complete(or even half) period is identical for both in-phase and antiphase signals, an acquisition time much shorter than / 2j will clearly favor the in-phase over the antiphase signal in terms of S/N. This difference in sensitivity is further increased46 limited dynamic range of NMR ADCs, additional solvent suppression has to be performed before digitization (i.e., presaturation). If the DQ filtering is done with pulsed field gradients (PGFs) instead of phase cycling, then this suppresses the solvent signals before hitting the digitizer. However, inserting PGFs into the DQF-COSY sequence causes other problems (additional delays and r.f. pulses, phase distortions, non-absorptive lineshapes, additional 50 % reduction of S/N). With the normal COSY sequence, they result in gigantic dispersive diagonal signals obscuring most of the 2D spectrum. Intensity of cross- and diagonal peaks In the basic COSY experiment, diagonal peaks develop with the cosine of the scalar coupling, while cross-peaks arise with the sine of the coupling. Theoretically, this does not make any difference (FT of a sine wave is identical to that of a cosine function, except for the phase of the signal). While this is normally true for the relatively high-frequency chemical shift modulations (up to several 1000 Hz), the modulations caused by scalar coupling are of rather low frequency (max. ca. 20 Hz for JHH), with a period often significantly shorter than the total acquision time. Time development of in-phase (cos pJt1) and antiphase (cos pJt1) terms, with W1 = 50 Hz, J = 2 Hz, for T2 = 10 s (left) and T2 = 0.1 s (right). While the total signal intensity accumulated over a complete (or even half) period is identical for both in-phase and antiphase signals, an acquisition time much shorter than 1 /2J will clearly favor the in-phase over the antiphase signal in terms of S/N. This difference in sensitivity is further increased