Convection-compensating PGSE experiment incorporating excitation-sculpting water suppression (CONVEX).

We present a new diffusion experiment which provides simultaneous suppression of an on-resonance solvent peak and compensation for convection. The experiment, which we name CONVEX, exploits similarities between two functionally different pulse sequences to enable the same sequence to be used simultaneously for two different purposes. The CONVEX pulse sequence combines a double-echo PGSE with double excitation-sculpting water suppression, using unequal gradient pulse-pair amplitudes (g1 and g2) and unequal diffusion intervals (Delta1 and Delta2). Convection compensation is achieved by setting g1:g2 = Delta2:Delta1. The new experiment provides the spectral quality, flat baseline, and water-suppression power characteristic of excitation-sculpting experiments, combined with excellent compensation for convection. The resulting Stejskal-Tanner plots are linear over a greater range of signal attenuation than in the absence of water suppression. Possible applications include protein NMR; NMR of cellular or colloidal systems; and the monitoring of technological processes.