Convection compensation in gradient enhanced nuclear magnetic resonance spectroscopy

Compensation of convection artifacts in gradient-enhanced nuclear magnetic resonance spectroscopy is introduced. Natural convection caused by small temperature gradients over the sample volume can lead to significant loss of magnetization in gradient-enhanced nuclear magnetic resonance spectroscopy, sometimes to its complete extinction or partial inversion. Even when the effect is small, it still hampers a quantitative interpretation of spectra, e.g., nuclear Overhauser effect buildup curves. By using modified pulse and gradient sequences it is possible to avoid the interference of convection, which is demonstrated by way of two examples: GOESY and GROESY. The principle of convection compensation is applicable to a wide variety of gradient-enhanced nuclear magnetic resonance experiments, in particular those where the interval between a defocusing and a refocusing pulsed field gradient is relatively long. (C) 1998 Academic Press.