FLIPSY - A NEW SOLVENT-SUPPRESSION SEQUENCE FOR NONEXCHANGING SOLUTESOFFERING IMPROVED INTEGRAL ACCURACY RELATIVE TO 1D NOESY

A new method of solvent suppression is described, based on presaturati on in combination with volume selection; the name ''FLIPSY'' is propos ed for this sequence. A low-flip-angle pulse is used for excitation, i mmediately followed by two 180 degrees pulses, each of which is indepe ndently phase cycled through Exorcycle. The phase-cycled inversion pul ses achieve volume selection in a way similar to the widely used 1D NO ESY sequence, thereby largely eliminating any residual ''hump'' signal from the solvent, The two 180 degrees pulses combine to produce a net 360 degrees rotation for z magnetization and either a 180 degrees or a 360 degrees rotation for transverse magnetization, depending on the step in the phase cycle. This allows the overall flip angle of the seq uence to be controlled by adjusting the length of the initial excitati on pulse, It is demonstrated that this property allows one to choose f reely a suitable compromise between signal strength and integral accur acy when using FLIPSY, just as when using single-pulse excitation, Suc h a choice cannot be made when using 1D NOESY, since the effective fli p angle in that experiment is always 90 degrees, The application of FL IPSY to recording LC-NMR spectra is demonstrated. (C) 1996 Academic Pr ess, Inc.