Nonchromatographic analysis of polyphenols in red wine samples: Evaluation of front-face fluorescence spectroscopy and third-order multivariate calibration to quantify catechin and epicatechin

In this work, an analytical approach based on third-order multivariate calibration and front-face fluorescence spectroscopy to determine the levels of (+)-catechin and (-)-epicatechin in wine samples was evaluated. An extra reaction mode (pH gradient) was incorporated into excitation-emission fluorescence second-order data, leading to higher predictivity and selectivity for catechin detection. Application of a Multivariate curve resolution-alternating least squares (MCR-ALS) algorithm resolved the systems, even in the presence of uncalibrated interferences, and yielded suitable figures of merit. Through the method, the level of (+)-catechin was directly determined, and the concentration of (-)-epicatechin was determined by the difference in total catechins (Epi + Cat) between synthetic samples. Finally, the levels of catechin were satisfactorily determined in real wine samples at mg L^-1 levels with minimal sample treatment and in accordance with a reference method based on chromatographic separation.