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Break it up: Ordinarily, silica gel produces no separation in a mixture of aromatic molecules by HPLC; however, solid‐enhanced DOSY NMR spectroscopy succeeds in this task, although its separation capabilities concern just the spectral components. Chromatographic NMR spectroscopy may thus prove a simple complement to HPLC in favorable cases. MAS=magic‐angle spinning.

The diffusional properties of molecules in solution vary dramatically upon addition of a solid chromatographic phase. This effect can be monitored via pulsed-gradient spin-echo NMR used in conjunction with moderately fast rotation of the sample (high-resolution magic angle spinning) to produce exploitable spectra. The molecular diffusion coefficients observed in this condition are averages reflecting the equilibrium population distribution among the different phases. It is thus possible to use this information for investigating a crucial step of reversed-phase chromatography, namely, the partitioning of the analyte between different phases. In this work, we describe the evolution of the apparent diffusion coefficient of typical solutes for water/acetonitrile solvent mixtures of varying proportions.

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