DIRECT DETERMINATION OF EQUILIBRIUM DEUTERIUM-ISOTOPE EFFECTS AT NATURAL ABUNDANCE

A great variety of techniques has been used to study deuterium-protium partitioning in exchanging systems at equilibrium. In this context it is shown that the determination of site-specific isotope contents by H-2-NMR at natural abundance provides simple and direct access to thermodynamic isotope fractionation factors. This method avoids the recourse to deuterated species and therefore the approximations inherent in the analysis of complex isotopomeric mixtures. A number of slowly exchanging systems involving OH, NH, or SH groups and water offer suitable conditions (large chemical shift differences, moderate line widths, ...) for the relatively accurate determination of thermodynamic fractionation factors. Moreover multiple fractionations can be observed and compared in ternary mixtures.