Electrochemical Sensing of Tea Polyphenols by Chloramine-T Modified Electrodes: A New Approach

Antioxidant activities of tea samples vary depending on its polyphenolic content. This paper presents an electrochemical sensing system for fast detection of polyphenols in tea infusion using a redox reagent, chloramine-T. Three different transducers namely, screen-printed electrode (SPE), glassy carbon (GCE) and platinum (PtE) electrodeswere used. The electrochemical reactions included oxidation of polyphenols (>C-OH) to o-quinone (>C=O) and reduction of chloramine-T to p-toluene sulfonamide (p-TSA). An IR band at 1636 cm(-1) (stretching of carbonyl group, >C=O) of the reaction product confirmed reduction of chloramine-T. The oxidation potential was obtained from cyclic voltammetry on three different electrode systems. Amperometric measurements were conducted at optimum anodic potential. The disposable SPE exhibited the lowest detection limit of 0.674 mgL(-1) with coefficient of variation less than 2.3%, recovery range of 98-103% and excellent selectivity against interfering compounds. The results compared very well with observations through high performance liquid chromatography (HPLC). A distinct concentration pattern was observed when varieties of tea were tested for polyphenols content. The sensor could be utilized to assess the quality of different grades of tea and pricing. (C) 2015 The Electrochemical Society. All rights reserved.