Flow-injection biamperometry of pyrogallol compounds

A biamperometric method for the direct determination of pyrogallol compounds has been designed for flow-injection analysis. The method is based on the electrocatalytic oxidation of pyrogallol compounds at one pretreated platinum electrode and the reduction of platinum oxide at the other pretreated platinum electrode to form a biamperometric detection system with the applied potential difference of 10 mV. Three important compounds, pyrogallol, gallic acid and tannic acid, have been detected by the method. The linear relationships between currents and the concentrations of pyrogallol, gallic acid and tannic acid are obtained over the range 1.0×10−6–1.0×10−4, 1.0×10−6–1.0×10−4 and 1.0×10−6–2.0×10−4 mol l−1 with the detection limit of 6.0×10−7, 6.0×10−7 and 8.0×10−7 mol l−1 (S/N=2), respectively. The R.S.D. observed for 30 successive determinations of 5.0×10−5 mol l−1 pyrogallol, gallic acid and tannic acid are 1.9, 2.5 and 2.0%, respectively. Most ions and organic compounds tested are found not to cause significant interference in the determinations. The method is simple, selective and efficient (180 h−1), performing well as a routine assay, and has been validated by the determination of pyrogallol compounds in tea and Chinese gall.