Dosy

Dosy, usually written DOSY in uppercase, refers to Diffusion-Ordered Spectroscopy, an analytical technique used in nuclear magnetic resonance (NMR) spectroscopy. DOSY separates signals in a mixture according to the translational diffusion coefficients of the solutes, yielding a two-dimensional spectrum in which one axis shows the chemical shifts and the other shows diffusion coefficients. The diffusion information is obtained by applying pulsed-field gradient sequences and analyzing signal attenuation through the Stejskal–Tanner equation, which relates gradient strength and diffusion to observed signal intensity. Differences in diffusion coefficients correlate with molecular size, shape, solvent interactions, and aggregation state, enabling researchers to distinguish coexisting species without physical separation.

Development and scope: DOSY emerged in the late 1980s and 1990s as an extension of diffusion NMR methods and has since become a routine tool in chemistry, biochemistry, and materials science. Variants of the technique use different gradient schemes, including pulsed-gradient spin-echo (PGSE) and stimulated-echo (PFGSE) approaches, to accommodate a range of samples and instrument configurations.

Applications and interpretation: Common uses include characterizing complex mixtures, monitoring reactions, estimating molecular sizes, studying binding events, and investigating aggregation in solutions. Signal assignments are aided by comparing measured diffusion coefficients with those of known standards or by analyzing relative diffusion behavior within the 2D DOSY map.

Limitations: DOSY has reduced resolution when species have similar diffusion properties, and accuracy depends on sample quality, gradient calibration, and instrument performance. Highly viscous solutions or low-concentration samples can further limit sensitivity.

See also: NMR spectroscopy, diffusion NMR, PGSE, Stejskal–Tanner equation.