SIMULTANEOUS DETERMINATION OF SPIN-LATTICE AND SPIN-SPIN RELAXATION-TIMES IN NMR - A ROBUST AND FACILE METHOD FOR MEASURING T-2 - OPTIMIZATION AND DATA-ANALYSIS OF THE OFFSET-SATURATION EXPERIMENT

The offset-saturation experiment is shown to be a robust method for the simultaneous measurement of T-1 and T-2 NMR spin relaxation times. Application of the method to the measurement of T-1 and T-2 in a sample of distilled water shows that the relaxation times determined by the offset-saturation method are in good agreement with those obtained by conventional inversion-recovery and CPMG experiments for T-1 and T-2, respectively. Errors in the relaxation times from the nonlinear-least-squares fit to the experimental data are on the order of 5%, provided that the irradiating field gamma B-2 is well calibrated and the sampling points are judiciously chosen. These errors are determined from the intersection of the appropriate parameter axis by the 95% confidence interval tangent. In the limit of small decoupler flip angles, the gated homodecouplers of high-resolution NMR spectrometers can be used as the RF irradiation source. The calibration of gamma B-2 can be performed simply and precisely using the single-spin double-resonance experiment, which is shown to be a generalization of the Bloch-Siegert shift effect. A simple qualitative guideline for optimization of the choice of irradiation resonance offsets and preacquisition delay times is derived from the partial-derivative criteria outlined here. (C) 1994 Academic Press, Inc.