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This paper presents the application of directly coupled capillary high-performance liquid chromatography (capillary HPLC) and proton high-field nuclear magnetic resonance spectroscopy (NMR) for structural elucidation of a so-far unknown kitol isomer. One- and two-dimensional continuous- and stopped-flow NMR spectra were recorded in a 180 μm i.d. capillary, corresponding to a detection volume of only 200 nL. Unequivocal structural assignment on the basis of 1D and 2D stopped-flow capillary HPLC-NMR experiments was performed. The kitol isomer mixture was present in a sample of thermally isomerized retinyl acetate and separated on a capillary column.

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SUMMARY: Copolymers of styrene and ethyl acrylate are prepared by radical polymerization and analysed with respect to microstructure by means of nuclear magnetic resonance. Using 13 C NMR, the compositional styrene-and ethyl acrylate-centered triads can be determined and compared to theoretical values. Good agreement between experimental and calculated triad concentrations are obtained for styrene-rich copolymers. Ethyl acrylate-rich copolymers exhibit significant deviations from the calculated values in particular for the ethyl acrylate homotriads. Using on-line coupled SEC-1 H NMR, the chemical composition across the molar mass axis can be monitored. It is found that ethyl acrylate-rich copolymers exhibit a broader molar mass and chemical composition distribution than styrene-rich copolymers. The results indicate that the block character of the copolymers with respect to ethyl acrylate units increases with increasing molar mass.