HPLC-SPE-NMR in studies of medicinal plants and herbal products

Hyphenated NMR spectroscopy is a state-of-the-art method for rapid and rigorous determination of natural product structures in plant extracts without isolation of the individual components in the classical sense. Among hyphenated NMR techniques, HPLC-SPE-NMR is the most convenient and superior in terms of quality of data, the most serious limitation being problems with solid-phase extraction of highly polar but nonionic species. The technique is particularly important in projects aimed at discovery of new chemical entities in medicinal plants, e.g., in connection with natural product discovery of novel pharmacologically active compounds. Moreover, studies related to standardization and uniformity of herbal products, performed either using metabolomic techniques or traditional methods, can benefit from support by hyphenated NMR experiments. HPLC-SPE-NMR work can be performed either using a flow NMR probe or a microtubes, and will benefit from increased sensitivity of cryogenically cooled probes. Examples of use of HPLC-SPE-NMR in analysis of medicinal plants and herbal products will be shown.