Total phenolic and tannins determination: a modification of Ph. Eur. 2.8.14 for higher throughput

A principle mostly being used to quantify phenols and tannins is the Folin-Ciocalteu's reagent method described in the European Pharmacopeia's method 2.8.14. Aim of the present study was to simplify this procedure in order to handle larger sample numbers. By changing the wavelength, the amounts of reagents, miniaturizing the setting to microtiter scale and changing the incubation time before measurement, the Ph. Eur. method 2.8.14 was optimized for a larger number of experiments. Calibration curves and time kinetics with different phenolic compounds (catechol, procyanidin B1, gallic acid, (+)-catechin, tannic acid, salicylic acid, ferulic acid) were determined. In addition, the absorbance of a 1 M solution was calculated by extrapolation of each calibration curve, to examine correlations due to the reaction's stoichiometry. Furthermore, the repeatability concerning herbal samples was investigated using Quercus cortex. The method was validated concerning its repeatability, robustness, linearity and reproducibility. Using this method, at least 120 samples can be handled per day by one person to quantify the total phenolic and tannin content.