JOURNAL OF MAGNETIC RESONANCE 75,352-357 (1987) Water Suppression Using a Combination of Hard and Soft Pulses d I

Numerous methods are available for suppmsion of the H20 resonance in the NMR spectra of water-soluble compounds. These methods include presaturation ( I, 2), ex-citation with a soft pulse (3) or a Re&eld pulse (4) , rapid scan correlation (51, binomial hard-pulse sequences (6-9), and methods that exploit the different relaxation char-acteristics of H20 and soiute protons (10-13). In recent years, the binomial hard-pulse sequences and variations thereof ( I # , 15) have become most WideIy used. Morris and Smith (16) showed that the binomid sequences can be combined with a single non-selective 90 " pulse to provide an excitation spectrum which has nearly maximal ex-citation over a wide frequency range except for a narrow region around the H20 resonance which has near-zero excitation. The phase distortions resulting from this type of excitation are severe which leads to problems when this type of composite pulse is usad in phasesensitive two-dimensional NMR experiments. Levitt and Rokrts (17) very recently proposed a new hard-pulse sequence which has a much weaker phase dependence across the spectrum whle still providing good water suppression. However, the remaining small phase distortions, which present no problem in I