Composite pulsed field gradients with refocused chemical shifts and short recovery time

An improved self-compensating pulsed held gradient (PFG) technique that com bines antiphase gradient pairs with broadband frequency-modulated 180 degre es pulses is proposed. The antiphase gradient pairs lead to superb system r ecovery. In addition, evolution under chemical shift and heteronuclear J co upling are refocused during the PFG, making it appear effectively instantan eous. This new approach makes it possible to obtain high-resolution-phase-s ensitive 2D spectra for the PFG version of many experiments such as COSY, D QF-COSY, and HSQC without adding extra compensating delays or pulses. While reasonable suppression of unwanted magnetization is achieved, this method also gives satisfactory retention of desired signals. As a bonus, the field -frequency lock is not perturbed during the experiments. (C) 1999 Academic Press.