Determination of some hydroxybenzoic acids and catechins in white wine samples by liquid chromatography with luminescence detection

A liquid chromatographic method with luminescence detection for the determination of eight phenolic compounds is reported. The method involves postcolumn derivatization with terbium(III). This derivatization is based on the reaction between phenolics and terbium(III) to form luminescent chelates, which were determined at lamda ex 295 and lamda em 545 nm using the fluorescence mode. The long wavelength emission of lanthanide chelates can minimize interferences from background sample matrix, which usually emit at shorter wavelengths. Also, the chromatographic separation allows the individual determination of phenolics, which cannot be done using the direct measurement of the fluorescence of their corresponding terbium chelates. Dynamic ranges of the calibration graphs and detection limits, obtained with standard solutions of analytes were (microg/mL): gallic acid (0.9-40, 0.3), protocatechuic acid (0.05-7, 0.016), catechin (0.2-40, 0.07), vanillic acid (0.25-40, 0.08), p-hydroxybenzoic acid (0.8-40, 0.25), syringic acid (0.17-40, 0.05), epicatechin (0.3-40, 0.09) and salicylic acid (0.07-12, 0.02). The precision was established at two concentration levels of each analyte and expressed as the percentage of RSD with values ranging between 1.0 and 6.5%. The practical usefulness of the method was demonstrated by the analysis of white wine samples, which were diluted two-fold and directly injected into the chromatographic system. The recovery values obtained ranged between 93.3 and 108.0%.