在HAc溶液中，柠檬酸对NO2-催化KBrO3氧化苯胺蓝的褪色反应具有抑制作用，阳离子表面活性剂苄基三乙基氯化铵对此体系有强烈增敏作用，据此建立了阻抑动力学光度法测定痕量柠檬酸的新方法。研究了吸收光谱、试剂用量、干扰离子等因素的影响，测定了动力学参数。在最佳实验条件下，阻抑反应与非阻抑反应体系在600 nm处的吸光度差值与柠檬酸的质量浓度在4~128 μg/L范围内呈良好线性关系，检测限为3.09×10-6 g/L。催化反应为动力学零级反应，表观活化能为138.2 kJ/mol，反应速率常数为2.16×10-3 mol /Lmin。在表面活性剂存在下，灵敏度提高2.6倍。此法用于汽水中柠檬酸的测定，结果满意。

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．