RF MICROCOIL DESIGN FOR PRACTICAL NMR OF MASS-LIMITED SAMPLES

This paper addresses practical issues involved in obtaining high resol ution H-1 NMR spectra from samples containing less than 10 nmol, Solen oidal microcoils have been constructed to: (a) assess the effects of m agnetic susceptibility mismatches at 500 MHz, (b) increase the concent ration sensitivity of microcoil probes, (c) incorporate a lock channel for 2D experiments and long 1D acquisitions, and (d) assess the total amount of the sample required (with respect to the coil length) to av oid line broadening due to edge effects. Compared to previously publis hed microcoil results, sample volumes have been increased by a factor of 20 with a concomitant decrease in the required concentration (5-20 mM), Perfluorocarbon susceptibility matching remained effective at 500 MHz, allowing acquisition of high resolution NMR spectra, A lock chan nel has also been successfully incorporated in microcoil probes. The l imits of detection for sucrose with a 10 min acquisition time were fou nd to be 17.8 and 34.1 pmol for the single and double resonance coils, respectively. A sample length of approximately 10 times than that of the coil was required to avoid magnetic susceptibility artifacts. (C) 1998 Academic Press.