INTRODUCTION

WATERGATE (1) is a solvent suppression method using gradients that applies a selective non-excitation sequence, conventionally to the read pulse of an experiment. Effective water suppression of at least two orders of magnitude can be routinely achieved with NOESY and ROESY spectra. However, when applied to Double Quantum Filtered (DQF) COSY (2) and to a lesser extent TOCSY experiments, it is difficult to obtain the same level of suppression. This is considered (3) to be due to the absence of a period during which radiation damping can help return the magnetisation back to +z prior to the read pulse. If the excitation profile of the final pulse has a region of non-excitation at the water frequency, the state of the water magnetisation after this pulse may be along the -z axis or even transverse, depending upon the stage of the phase cycle. The behaviour of the water magnetisation from these states adversely affects its removal by phase cycling.