Densitometric determination of (+)-catechin and (−)-epicatechin by 4-dimethylaminocinnamaldehyde reagent

We report the optimization of a sensitive, selective and robust derivatization method using 4-dimethylaminocinnamaldehyde (DMACA) for densitometric determination of (+)-catechin and (−)-epicatechin. The separation of these compounds was achieved by thin-layer chromatography (TLC) on cellulose plates developed with water. With DMACA in HCl, both compounds gave blue bands, while under the same conditions, vanillin produced a fast fading red coloration of bands. Quantitation at 655 nm showed that for both compounds the calibration curve was linear from 2 to 12 ng and polynomial from 2 to 30 ng, and the repeatability of chromatography of 20 ng was 3.5% (RSD, n = 6). The visible limit of detection of both standards was 1 ng, but the densitometric limit of detection was lower (0.2 ng). The optimized DMACA reagent is superior to the more frequently used vanillin reagent and is applicable also for determination of mixtures containing other catechins ((−)-catechin, (−)-epicatechin gallate, (−)-epigallocatechin gallate, procyanidin A2, procyanidin B1 and procyanidin B2).