Abstract:A new inhibitory catalytic kinetic spectrophotometric method for the determination of trace amount of citric acid was developed based on that citric acid can inhibit the discoloration of the catalytic oxidation reaction of Spirit Blue with KBrO3 by NO2- in the presence of HAc solution using cationic surfactant of Benzyltriethylammonium chloride as an sensitizer. The effects of the factors such as absorption spectra, acidity, concentrations of reagent and coexisting ions, on the reaction are discussed and the kinetic conditions were studied. Under the optimum conditions, good linear relationship was obtained between absorbance difference (ΔA ) of the inhibited system and non-inhibited system at 520 nm and the concentration of citric acid in the range of 4~128 μg/L with the detection limit of 3.09×10-6 g/L. The catalytic reaction was the zero-order reaction and apparent activation energy of the catalytic reaction 138.2 kJ/mol, and the reaction rate constant was corresponding to 2.16×10-3 mol/Lmin. The sensitivity was increased by 2.6 times than in the absence of the surfactant. The method can be used for the determination of citric acid in water with satisfactory result．
