Diffusion-Ordered Spectroscopy

Abstract

Diffusion-ordered spectroscopy (DOSY) is a mixture analysis technique based on pulsed field gradient spin (PFGSE) or stimulated (PFGSTE) echo measurements. In such experiments, the measured signal intensity depends on timing, diffusion coefficient, and gradient amplitude, so measurements made with a range of gradient strengths allow the diffusion coefficients for different signals to be determined. Since the diffusion coefficient is characteristic of a given molecule, the NMR signals from species of different sizes can be distinguished. The name DOSY refers to the use of a set of diffusion-attenuated spectra to synthesize a multidimensional spectrum in which signals are spread out according to diffusion coefficient in one of the dimensions. Thus, in an ideal 2-D DOSY spectrum, all the signals of a given species appear at the same diffusion coefficient, allowing the NMR spectra of complex mixtures to be analyzed. In this article, the principles of DOSY are explained, practical methods of data acquisition and analysis are discussed, and examples are given both of 2-D and 3-D DOSY spectra and of multivariate analysis of DOSY data. Keywords: DOSY; pulsed field gradients; diffusion; diffusion-ordered spectroscopy