CONVECTION COMPENSATION IN GRADIENT-ENHANCED NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Compensation of convection artifacts in gradient-enhanced nuclear magn etic resonance spectroscopy is introduced. Natural convection caused b y small temperature gradients over the sample volume can lead to signi ficant loss of magnetization in gradient-enhanced nuclear magnetic res onance spectroscopy, sometimes to its complete extinction or partial i nversion. Even when the effect is small, it still hampers a quantitati ve 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 compens ation is applicable to a wide variety of gradient-enhanced nuclear mag netic resonance experiments, in particular those where the interval be tween a defocusing and a refocusing pulsed field gradient is relativel y long. (C) 1998 Academic Press.