Hyphenation of high performance liquid chromatography with nuclear magnetic resonance spectroscopy for the characterization of beta-carotene isomers employing a C30 stationary phase.

The hyphenation of HPLC together with NMR spectroscopy proves advantageous for the structure elucidation of oxidation- and UV-sensitive compounds such as beta-carotene isomers. In the closed-loop HPLC-NMR system, degradation or isomerization of separated compounds is largely hindered. With the help of 3-microm C30 stationary phases a better separation efficiency towards the different beta-carotene cis/trans isomers could be obtained in comparison to a 5-microm material, resulting in sharper peaks and a better resolution of all compounds. This effect greatly facilitated the structure determination of the isomers by HPLC-NMR coupling. Due to the introduction of a superior stationary phase, the structure of seven cis-isomers of beta-carotene could thereby be determined employing the stopped-flow HPLC-1H-NMR mode.