Evaluation of benchtop NMR Diffusion Ordered Spectroscopy for small molecule mixture analysis.

Diffusion Ordered Spectroscopy (DOSY) is an attractive method for analyzing chemical mixtures in the liquid state because it separates spectra by the molecular weight of the associated molecule. It has been compared with hyphenated chromatographic and analytical methods such LC-MS and has broad potential in servicing those same applications including forensics, reaction analysis, quality control, and fraud detection. Benchtop NMR can collect quality spectra on small molecules, however, lacks the chemical shift dispersion of high field instruments, can suffer from spectral overlap common in mixtures, and the diminished sensitivity of the lower field compounds these problems. In this work, we show that existing high field pulse sequences and processing methods perform well at 43 MHz. Spectra from molecular mixtures where the constituents had 20% differences in diffusion coefficients and significant overlap were able to be matched to a bespoke spectral library and identified correctly. In addition, spectra from mixtures with constituents that have severe overlap in the spectrum and differ by 50% in diffusion coefficients were also able to be match and identified correctly. The combination of benchtop NMR and easy implementation of modern pulse sequences and processing show promise of bringing these useful methods to chemistry laboratories in research and industrial environments.

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