RAPID-PULSING ARTIFACT-FREE DOUBLE-QUANTUM-FILTERED HOMONUCLEAR SPECTROSCOPY - THE 2D-INADEQUATE EXPERIMENT REVISITED

Rapid pulsing artifacts are observed in the conventional phase-cycled carbon-13 2D INADEQUATE experiment. By using the product operator form alism, it is shown that they result from the effects of imperfect 90 d egrees and 180 degrees excitation pulses on the most abundant molecule s containing only one isolated carbon-13 nucleus. The labeled longitud inal magnetization remaining at the end of one scan is recycled by the subsequent acquisition, giving rise to multiple-quantum (p = 0, +/-1, +/-2,...) artifacts in the F-1 dimension. By considering pairs of sca ns instead of single scans, a new phase cycle is proposed. It is based on a scheme for compensating for imperfections in the excitation clus ter by a proper combination of the pulse phases in two consecutive sca ns, Because the artifacts are 90 degrees out of phase compared to the desired signal, a concomitant rearrangement of the receiver phase achi eves suppression of all unwanted signals. Experiments are presented on menthol dissolved in CDCl3 as a test compound. Improvements in spectr um quality as well as increased sensitivity are discussed. (C) 1998 Ac ademic Press.