Improved residual water suppression: WET180.

Water suppression in biological NMR is frequently made inefficient by the presence of faraway water that is located near the edges of the RF coil and experiences significantly reduced RF field. WET180 (WET with 180 degrees pulse-toggling) is proposed to cancel the faraway water contribution to the residual solvent signal. The pulse sequence incorporates a modification of the last WET selective pulse to accommodate insertion of a toggled 180 degrees inversion pulse so that the original WET selective pulse angles are effectively preserved. Compared with existing WET methods, WET180 has the advantages of easy implementation, improved residual water suppression, clean spectral phase properties, and good signal intensity retention. WET180 is expected to be most useful in observing resonances close to water in samples containing biological molecules. In addition, the principle of WET180 can be applied in multidimensional experiments to improve residual water suppression and reduce artifacts around water.