Reference Flow Injection Analysis of Trace Amounts of Tannin with Inhibited Kinetic Spectrophotometric Detection

Abstract

A simple and highly sensitive reference flow injection inhibited kinetic spectrophotometric method is proposed for the determination of trace tannin in tea and wine samples. The method was based on the enhanced sensitivity of cetylpyridinium bromide on the redox reaction between Eosine Y and KBrO3, and on inhibitory effect of tannin on the same reaction in the sulphuric acid medium. The resulting red complex product was stable in sulphuric acidic medium and has a maximum absorption at 540 nm. The linear response range and detection limit are 0.010-0.45 mg L-1and 4.82μg L-1respectively. The sampling frequency was 20 samples per hour. The relative standard deviation for 11 determinations of 0.10mg L-1tannin acid was 1.78% and values of recovery in the rang of 96.7%-107.3%.The proposed method has been successfully used to determine tannin in tea and wine samples. The results obtained were compared with those provided by the FolinDenis method.