The spectro-electro array: A novel platform for the measurement of secondary metabolites in botanicals, supplements, and beverages

Plants contain an amazingly diverse range of secondary metabolites, many of which are purported to offer health benefits. The challenge for the analytical chemist for the measurement of these compounds is two-fold: first, to develop assays that can accurately discriminate between compounds that often have similar physicochemical characteristics; second, to analyze such compounds in complicated matrices including botanicals, supplements, and beverages. Gradient HPLC with diode array detection (DAD) is often used for the determination of natural products. However, this approach often suffers from a lack of specificity as compounds with similar structures may co-elute chromatographically and cannot be deconvoluted spectrally. Furthermore, this technique lacks sensitivity limiting its use for the study of natural product metabolism in animals and humans. Coulometric electrochemical array detection, on the other hand, is selective, being able to distinguish between subtle changes in chemical structure and, with sub pg LODs, can be used to examine natural product absorption and metabolism. The combination of DAD and coulometric EC array detection extends the range of compounds measured by either technology alone. The technique has been used to resolve and quantify specific phytochemicals in crude extracts of a variety of natural products supplements, (e.g., ginseng, black cohosh and ginko) beverages (black and green tea), culinary herbs (oregano, rosemary) and spices (clove, nutmeg). Changes in the pattern of metabolites, when evaluated using chemometric modeling software, can be used to study: product authenticity, adulteration, contamination, and composition, and in the case of wine and fruit juice, the effect of growing region and differences between varietals.