ELIMINATION OF LONGITUDINAL MULTIPLE-QUANTUM ARTIFACTS IN 2D COSY SPECTRA

A detailed analysis of phase-cycling procedures in COSY 2D NMR experiments is described. It is shown that a phase-cycling scheme, originally proposed by Rinaldi and Iverson (J. Magn. Reson. 92, 528, 1991) can be used to eliminate all longitudinal MQ artifacts of even order Delta m = 0, +/-2, +/-4, etc., exactly. In addition, it is demonstrated that in rotation-sensitive experiments, designed to produce an N-type Delta m = -1 peak, the odd-order multiple-quantum artifact Delta m = +3 appears as a P-type peak. Thus rotation-sensitive COSY experiments can be used to discriminate against Delta m = 0, +/-2, +/-3, and +/-4 MQ artifacts. The theoretical results are confirmed experimentally, using a nominally isolated spin-1/2 ensemble, which can be made to generate MQ artifacts as high as Delta m = +/-5. (C) 1994 Academic Press, Inc.