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Analytical Chemistry

NMR Technique Monitors Liquids And Solids

‘CLASSIC NMR’ approach maps evolution of crystallization by analyzing both phases

by Stu Borman
July 28, 2014 | A version of this story appeared in Volume 92, Issue 30

A new approach called CLASSIC NMR isn’t actually classical at all, in that it’s the first NMR technique that can watch exactly how crystallization processes evolve by monitoring liquid- and solid-state NMR spectra essentially simultaneously. In the past few years, Kenneth D. M. Harris and coworkers at Cardiff University, in Wales, developed a solid-state NMR technique designed to selectively observe the solid phase and ignore the liquid phase in solid-liquid systems, such as those that exist during crystallization from solution. Now, they have revised it into an approach that examines crystallization from both sides (Angew. Chem. Int. Ed. 2014, DOI: 10.1002/anie.201404266). In the CLASSIC (combined liquid- and solid-state in situ crystallization) NMR technique, the researchers alternate between two different pulse sequences to record liquid- and solid-state NMR spectra. They demonstrate the technique by using it to study the time evolution of solution-phase species and the formation of various polymorphs (solid phases) in the crystallization of m-aminobenzoic acid. “The CLASSIC NMR experiment can be carried out on any standard solid-state NMR spectrometer, without requiring modification of the instrumentation,” the researchers note.


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