HETERONUCLEAR DOUBLE-QUANTUM-COHERENCE SELECTION WITH MAGNETIC-FIELD GRADIENTS IN DIFFUSION EXPERIMENTS

A 3.5-fold reduction in the magnitude of the magnetic-field-gradient pulses was achieved in a 31P NMR pulsed-field-gradient spin-echo experiment, used to measure the diffusion coefficient of a phosphorus-containing solute; this reduction involved a variant of a heteronuclear ′inverse-detection′ pulse sequence. The attendant eddy currents, set up in the conducting elements of the probe and magnet were reduced because of the smaller current required in the field-gradient coils. Linear magnetic-field gradients were also used in the pulse sequence to select heteronuclear double-quantum coherences, thus obviating the requirement for extensive phase cycling and potential dynamic range problems, because any signal that arose from magnetization that had not been double-quantum coherent was "spoiled" in the experiment prior to signal detection. The utility of the pulse sequence and the necessary modifications to the standard Stejskal and Tanner analysis that are required for data from the experiment are illustrated with the heteronuclear-coupled, 1H-31P, system of neutralized phosphorus acid [HPO(OH)2] in water. © 1993 by Academic Press, Inc.