J-compensated PGSE : an improved NMR diffusion experiment with fewer phase distortions

Peak distortion caused by homonuclear 1H J-coupling is a major problem in many spin-echo-based experiments such as pulsed gradient spin-echo (PGSE) experiments. Although peak phase distortions can be lessened by the incorporation of anti-phase purging sequences, the sensitivity is substantially decreased. Techniques for lessening the effect of homonuclear J-coupling evolution in spin-echo-based experiments have been investigated. Two potentially useful candidates include a J-compensated inversion sequence that is efficient over a wide range of J-coupling values and a pulse sequence that refocuses homonuclear J-evolution during the spin-echo. The latter was found to work superbly on samples containing two spin (AX or AB) systems and still provided significant advantage over the standard method on samples containing more complicated spin systems. Implementation of this J-refocusing technique into a PGSE-type experiment (J-PGSE) leads to dramatic improvement of spectra and easier data analysis. The J-PGSE sequence should find applications in many diffusion studies where the PGSE-type method is required and should be a viable alternative to PGSTE especially in dilute samples due to its enhanced sensitivity.