An amperometric flow-injection assay was proposed for measuring the levels of tannin in tea. Electrode fouling owing to electro-oxidation
of tannin could be efficiently avoided by utilizing ferricyanide as an oxidant to pre-oxidize tannin for indirect quantification without electrode
modification. Appropriate concentrations of ferricyanide were pre-mixed with tannic acid and then measured by a platinum electrode in an
electrochemical flow cell. The effects of working potential and flow rate on amperometric response were investigated, and the optimal condition
was obtained when theworking potentialwas−0.1V(versus Ag/AgCl) and the flowratewas 2.28mLmin−1 in thiswork. The linear detection range
for tannic acid could be effectively adjusted according with application demand, and the results of this study indicated two ranges of 10–50 gmL−1
and 100–500 gmL−1 (CV < 5%, n = 3). Beverage samples of tea with various fermentation degrees were measured (15 samples h−1) and verified
with Folin–Ciocalteau method (r = 0.9794) as well as the ferrous tartrate method (r = 0.9918).
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