A new flow-injection spectrophotometric method for the determination of tannins in tea and beer using iron(III) and 1,10-phenanthroline

Abstract

A new flow-injection spectrophotometric method for the determination of tannins in tea and beer based on the reduction of Fe(III) to Fe(II) by tannins and the subsequent formation of the coloured complex Fe(II)-1,10-phenanthroline is proposed. The FIA set-up used is controlled by a personal computer running appropriate software for automatic sample injection and data acquisition and processing. The calibration curve obtained is linear between 0–30 mg litre −1 gallic acid and the relative standard deviation for a standard containing 10 mg litre −1 gallic acid is 0·7% ( n = 10). The sample throughput achieved is 60 sample h −1. Unlike the batch method, on which it is based, the proposed method requires no sample pretreatment in order to avoid interferences; it only involves appropriate dilution of the samples, and so provides more reliable results in a substantially shorter time.