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 analysis of aqueous mixtures. Pulsed field gradient NMR (PFG-NMR) experiments were performed with special provisions for minimizing the effects 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 molecular size. Contour plots were then constructed in which conventional 1D NMR spectra were displayed in one dimension and diffusion spectra in the other. Complete resolution of molecular species was obtained except when two components had essentially identical diffusion coefficients. The addition of surfactants at concentrations above their critical micelle concentrations permitted solutes to be resolved on the basis of their degree of solubilization in the micelles formed. DOSY is shown to be a powerful tool for the study of equilibria involving binding, absorption, and partitioning in more complex systems than previously considered accessible by conventional PFG-NMR methods.