Analysis of complex reacting mixtures by time-resolved 2D NMR.

Nuclear magnetic resonance (NMR) spectroscopy is a versatile tool for chemical analysis. Besides the most straightforward application to study a stable sample containing a single compound, NMR has been also used for the analysis of mixtures. In particular, the analyzed mixtures can undergo changes caused by chemical reactions. The multidimensional NMR techniques are especially effective in a case of samples containing many components. Unfortunately, they are usually too lengthy to be applied in time-resolved experiments performed to study mentioned changes in a series of spectral "snapshots." Recently, time-resolved nonuniform sampling (NUS) has been proposed as a straightforward solution to the problem. In this paper, we discuss the features of time-resolved NUS and give practical recommendations regarding the temporal resolution and use of the time pseudodimension to resolve the components. The theoretical considerations are exemplified by the application in challenging cases of fermenting samples of wheat flour and milk.