Cyclic voltammetry (CV), chronoamperometry (CA) and square wave voltammetry (SWV) were used to investigate electrocatalytic reductions of , , and 4-nitrophenol on carbon cloth modified by composite film of tungsten oxide (WO₃) and polyaniline (PANI). Results of amperometric experiments on WO₃/PANI modified electrode revealed good linear relationship between response currents of the electrode and concentration of , , and 4-nitrophenol in the range of 40 mmol/L～1.2 mmol/L, 0.12～20 mmol/L, 40 mmol/L～2.50 mmol/L and 50～400 mmol/L, respectively. The sensitivity and the detection limit (S/N＝3) for these species are 0.202 mA/(mmol/L), 4.8 mmol/L ( )|0.035 mA/(mmol/L), 23 mmol/L ( )|0.120 mA/(mmol/L), 5.9 mmol/L ( ) and 0.443 mA/(mmol/L), 8.8 mmol/L (4-nitrophenol).

Key words: tungsten oxide, polyaniline, electrocatalytic reduction, bromate, chlorate, nitrite, 4-nitrophenol