CONTROL OF SPINNING SIDE-BAND IN HIGH-RESOLUTION NMR-SPECTROSCOPY

The presence of spinning sidebands can severely compromise the detecti on of low molarity analytes. Spinning sidebands have traditionally bee n minimized by improving the magnetic field homogeneity and by varying the spinning of the sample in a linear fashion during data acquisitio n, The effect of the latter is to spread the spinning sideband intensi ty over a range of frequencies so that the final result is a spinning sideband whose shape reflects the distribution of spinning speeds. We have designed a customized profile of spinner speed variation that opt imizes the reduction of spinning sidebands, The customized profile is based on theoretical considerations of how the intensity of sidebands vary with the rate of sample rotation and also compensates for the mec hanical design of the spinner mechanism. The result is a unique combin ation of an exponential increase in gas flow rate to balance the theor etical considerations coupled with a strategically placed rapid change in air flow to annul the sluggish response of the spinning mechanism to acceleration. The resulting sideband shape is a broad, flat, square step in the baseline that is least likely to interfere with low molar ity analyte peaks. (C) 1998 Academic Press.