Chromatographic separations and liquid phase extraction/concentration of some polyphenolic compounds: a comparison between reverse phase and cation-exchange chromatography

Abstract

Chromatographic performance based on the use of a C₁₈ reverse phase and a LC-SCX cation-exchange column associated with UV absorption at 280 nm is optimized and compared for the simultaneous determination of resveratrol and other polyphenolic compounds with the aim to establish the best experimental conditions for the trace analysis of these substances. Under the optimized chromatographic conditions using a gradient acid mobile phase and acetonitrile as a modifier solvent, the elution of all injected compounds was completed in about 30 min of analysis and the detection limits (LOD) ranged between 20 nM and 120 nM. The regression analysis for most of the analyzed compounds shows linear ranges spanning over five orders of magnitude with correlation coefficients always ≥0.98. A liquid–liquid extraction procedure was optimized using three different extracting solvents such as methyl ethyl ketone, diethyl ether, and dichloromethane. The hydrophilic/hydrophobic character of the water/organic solvent was modulated by addition of NaCl salt. In order to ascertain the analytical potentialities of the investigated method, and in particular the performance of the extraction procedure, a wide variety of selected red wines were analysed. The average recoveries ranged between 73% and 103% for the analysed molecules, indicating both the practical absence of interfering peaks on the chromatographic separation and an appreciable capacity of extraction of polyphenolic acids from the wine matrices.