Heteronuclear radiofrequency field gradient NMR spectroscopy with a doubly tuned coil

A novel NMR method employing radiofrequency field gradients (B1 gradients) is demonstrated. This approach rests on a doubly tuned coil capable of generating B1 gradients at two different frequencies and is obviously suitable for heteronuclear experiments. It is illustrated by the selection of the 13C-1H longitudinal spin order in the simple two spin system of formic acid; the potentialities of the method are outlined.