Chemical reaction detection of catechins and proanthocyanidins with 4-dimethylaminocinnamaldehyde

An high-performance liquid chromatographic method with post-column derivatization is described which allows the specific detection of catechins and proanthocyanidins in crude extracts from plants and beverages. In the presence of concentrated sulphuric acid, 4-dimethylaminocinnamaldehyde can be employed as a selective reagent. The advantage of the reagent is that its condensation products with flavanols show maximum absorbance at about 640 nm. Other phenols, indoles and terpenes give reaction products with different absorbances or react very weakly. A 200-40 000 fold sensitivity was found for (-)-epicatechin as compared to other phenols and substituted indoles. Concerning the terpenes, this factor ranges from 4000 (for the aromatic thymol) to 2 · 10⁶.