Rapid-Pulsing Artifact-Free Double-Quantum-Filtered Homonuclear Spectroscopy

Rapid pulsing artifacts are observed in the conventional phase-cycled carbon-13 2D INADEQUATE experiment. By using the product operator formalism, it is shown that they result from the effects of imperfect 90 degrees and 180 degrees excitation pulses on the most abundant molecules containing only one isolated carbon-13 nucleus. The labeled longitudinal magnetization remaining at the end of one scan is recycled by the subsequent acquisition, giving rise to multiple-quantum (p = 0, +/-1, +/-2, ellipsis) artifacts in the F1 dimension. By considering pairs of scans instead of single scans, a new phase cycle is proposed. It is based on a scheme for compensating for imperfections in the excitation cluster by a proper combination of the pulse phases in two consecutive scans. Because the artifacts are 90 degrees out of phase compared to the desired signal, a concomitant rearrangement of the receiver phase achieves suppression of all unwanted signals. Experiments are presented on menthol dissolved in CDCl3 as a test compound. Improvements in spectrum quality as well as increased sensitivity are discussed. Copyright 1998 Academic Press.