Chromatography In An NMR Tube

Getting NMR spectral data on the product of a chemical transformation usually means separating the molecule from the reaction's starting material, intermediates, and side products via chromatography. Now, Sami Heikkinen and coworkers of the University of Helsinki, in Finland, have developed a way to resolve this witches' brew in an NMR tube using an inexpensive, commercially available polymer (Org. Lett., DOI: 10.1021/ol9001398). The method employs diffusion-ordered NMR spectroscopy, or DOSY, which separates the spectra of individual compounds in a mixture according to the compounds' diffusion rates. The researchers liken the technique's ability to separate analytes to thin-layer chromatography (TLC). Because insoluble silica—the stationary phase used in TLC—would severely compromise the quality of the NMR spectra, the researchers chose soluble polyvinylpyrrolidone as the "stationary phase" to enhance diffusion. "This method provides a fast, cheap, and simple technique to resolve the NMR spectra of complex mixtures," the authors write.