ANALYSIS OF MIXTURES BASED ON MOLECULAR-SIZE AND HYDROPHOBICITY BY MEANS OF DIFFUSION-ORDERED 2D NMR

Diffusion-ordered 2D NMR spectroscopy (DOSY) has been applied to the a nalysis of aqueous mixtures. Pulsed field gradient NMR (PFG-NMR) exper iments were performed with special provisions for minimizing the effec ts of pulse-induced eddy currents and with sample spinning during the data acquisition period. The FT PFG-NMR data sets were processed with the data inversion program SPLMOD to resolve and identify the solutes on the basis of diffusion coefficients that normally are related to mo lecular size. Contour plots were then constructed in which conventiona l 1D NMR spectra were displayed in one dimension and diffusion spectra in the other. Complete resolution of molecular species was obtained e xcept when two components had essentially identical diffusion coeffici ents. The addition of surfactants at concentrations above their critic al micelle concentrations permitted solutes to be resolved on the basi s of their degree of solubilization in the micelles formed. DOSY is sh own to be a powerful tool for the study of equilibria involving bindin g, absorption, and partitioning in more complex systems than previousl y considered accessible by conventional PFG-NMR methods.