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

Numerous methods are available for suppression of the Hz0 resonance in the NMR spectra of water-soluble compounds. These methods include presaturation (I, 2), ex-citation with a soft pulse (3) or a Redfield pulse (4), rapid scan correlation (5), binomial hard-pulse sequences (6-9), and methods that exploit the different relaxation char-acteristics of HZ0 and solute protons (10-13). In recent years, the binomial hard-pulse sequences and variations thereof (14, 15) have become most widely used. Morris and Smith (16) showed that the binomial 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 HZ0 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 used in phase-sensitive two-dimensional NMR experiments. Levitt and Roberts (I 7) very recently proposed a new hard-pulse sequence which has a much weaker phase dependence across the spectrum while still providing good water suppression. However, the remaining small phase distortions, which present no problem in 1