Influence of liquid phase composition on RP-HPLC and CZE of plant secondary metabolites

Plant secondary metabolites are organic compounds produced by plants, which are not involved in the growth, photosynthesis, reproduction and other primary functions of the plants but are believed to have a role in defence mechanisms, such as protection against herbivores, pests and pathogens. Phenolic compounds are one of the main classes of secondary metabolites and because are widely distributed in the plant kingdom form an integral part of human diet. In addition to confer specific sensorial characteristics to plant-derived foods and/or beneficial effects on human health, phenolic compounds are also biomolecules with pharmacological activity employed in phytotherapeutic medicine. The identification and quantification of these target compounds in plants tissues and agro-food matrices is a challenging task, continuously requesting the development of more robust, efficient and sensitive instrumental analytical techniques. This communication discusses fundamental and practical aspects of both reversed phase high performance liquid chromatography (RP-HPLC) and capillary zone electrophoresis (CZE) tailored for the analysis of plant secondary metabolites. The communication reports the results of our recent studies carried out to evaluate the influence of various operational parameters and experimental conditions employed in CZE and in RP-HPLC on the separation performance of phenolic compounds and other secondary metabolites in agro-food matrices. Because both RP-HPLC and CZE require the use of a liquid phase, whose composition plays a fundamental role on their separation mechanisms and performance, most of our investigations has been focused on the selection of the proper composition of the liquid phase, which, in the case of RP-HPLC, has been optimized by a quality by design approach.