在0.04 mol·L-1硫酸介质中,甲醛对溴酸钾氧化甲基橙的反应具有显著催化作用,且在甲醛质量浓度为0.08~0.48 mg·L-1之间与在510 nm测得的吸光度之间呈线性关系,其线性回归方程为ΔA=1.563 2 C-0.044 1(式中C为甲醛质量浓度,以mg·L-1表示),其相关系数为0.998 5,方法的检出限为5.18×10-3mg·L-1.对此反应的动力学性质也作了研究,甲基橙的氧化反应为0.5级反应,甲醛的催化反应为一级反应,测得其表观活化能为74.53 kJ·mol-1.将所提出的方法应用于几种水样中痕量甲醛的测定,计算得分析结果的相对标准偏差(n=8)均小于0.9%,测得回收率在95.1%~104.9%之间.方法所测得的结果与乙酰丙酮光度法测得的结果相吻合.

In a weakly acidic medium of about 0.04 mol·L-1 H2SO4,the oxidation of methyl orange by potassium bromate was significantly catalyzed by formaldehyde. Linear relationship was kept between the magnitude of decrease in absorbance at 510 nm and the concentration of formaldehyde in the range of 0.08-0.48 mg·L-1 corresponding to the linear regression equation ΔA=1.563 2 C-0.044 1 (C: mg of HCHO per L) and with correlation coefficient of 0.998 5. Detection limit of the reaction was found to be 5.18×10-3mg·L-1. Kinetic behavior of the reaction was studied. Oxidation reaction of methyl orange was found to be of 0.5th order and catalytic reaction of formaldehyde to be of 1st order. Apparent activation energy of the reaction was determined and the value obtained was 74.53 kJ·mol-1. The proposed method was used in the determination of traces of formaldehyde in several water samples,giving values of RSD′s (n=8) less than 0.9%,and recoveries in the range of 95.1%-104.9%. Results obtained by this method were in consistency with the results found by the acetylacetone photometry.