Improvements in complex mixture analysis by NMR: DQF-COSY iDOSY

Diffusion-ordered NMR spectroscopy (DOSY NMR) is a highly useful tool for the study of complex mixtures via NMR. Often, spectral overlap limits the ability of obtaining cleanly separated subspectra of the components due to inherently instable multiexponential fits or data inversion procedures. Three-dimensional DOSY variants offer the advantage of separating individual peaks in an additional dimension, such that robust monoexponential fits to cross-peaks may be used to determine the diffusion coefficients with higher accuracy. For sensitivity reasons, methods based on proton nuclei are preferable. We show that a double-quantum-filtered COSY-DOSY experiment provides advantages over COSY-DOSY, while high signal-to-noise ratios are maintained. We demonstrate the viability of the technique by applying it to a solution of single-stranded DNA oligomers and to a mixture of unprocessed beeswax and decanol.