Flow injection-biamperometric determination of tannin in tea

Based on the flow injection-biamperometry for irreversible couple system, a method has been established for the determination of tannin in tea. Using two preanodized platinum electrodes, the biamperometric detection system was setup by coupling the oxidation of tannin at an electrode and the reduction of platinum oxide at the other. Under the applied potential difference of 0 V, the linearity between current and tannin concentration was obtained over the range 1.0 x 10(-6) similar to 1.0 x 10(-4) mol/L with the detection limit 6.0 x 10(-7) mol/L (S/N = 2). The relative standard derivation of 1.2% was obtained for 42 successive determinations of 1.0 x 10(-5) mol/L tannin. The procedure is superior to the current official method for its simplicity, high efficiency and high sensitivity, and has been used for the determination of tannin in commercial samples of green tea, jasmine tea, wulong tea and red tea with satisfactory results.