Comprehensive two-dimensional liquid chromatography in the analysis of antioxidant phenolic compounds in wines and juices

A novel comprehensive two-dimensional liquid chromatographic (LC×LC) system was developed for the quantification of antioxidant phenolic compounds in wine and juice. The system allows parts of the sample that are well separated in the first column to pass directly to the detector after the first column, while the rest of the sample proceeds to the second column. The optimised LC×LC system employed a combination of two C18 columns, the latter column with an ion-pair reagent (tetrapentylammonium bromide). The relative standard deviations (RSD) for the retention times were better than 0.01% in the first dimension and on average 6.3% in the second. The RSD values of the peak volumes varied from 3% (protocatechuic acid) to 13% (caffeic acid, n = 3, 10 μg/ml).