【摘要】 提出了催化动力学吸光光度测定铜的新方法 ,基于在 0 .0 5～ 0 .0 9mol· L-1硫酸介质中和 2 .0× 1 0 -3 mol·L-1氯化十六烷基吡啶存在下 ,Cu( )催化抗坏血酸还原邻甲氧基苯基重氮氨基偶氮苯。用固定时间法在 50 2 nm处监测催化反应。方法的线性范围为 0～ 2 8ng·ml-1,检出限( 3σ)为 0 .66ng· ml-1,摩尔吸光系数为 9.65× 1 0 5L· mol-1· cm-1。除 Fe( )外常见离子都不干扰测定。用 NH4 F掩蔽 Fe( ) ,方法直接应用于多种食品分析 ,结果与二乙基二硫代氨基甲酸钠萃取光度法相同 ,相对标准偏差为 2 .0 %～ 4.4% ( n=6)。非催化反应和催化反应在 3.0～ 8.0 min内为假零级反应 ,活化能分别为 1 56.1和 1 0 3.8k J· mol更多还原

【Abstract】 It is found that the reduction of o -methoxy-benzene diazoaminoazobenzene (MDAA) by ascorbic acid is catalyzed by trace amounts of copper(Ⅱ) ion in a H 2SO 4 medium of 0.05~0.09mol·L -1 and in the presence of 2.0×10 -3 mol·L -1 cetylpyridinium chloride. Based on this phenomenon, a sensitive photometric method for the determination of microamounts of copper in foodstuff is presented. The decrease of absorbance of MDAA by the reduction reaction is measured at 502nm at fixed time intervals. Linear relationship between Δ A and [Cu 2+ ] is found in the range of 0~28ng of Cu(Ⅱ) per ml of solution. The apparent molar absorptivity of this reaction is found to be 9 65×10 5L·mol -1 ·cm -1 , and its detection limit to be 0.66ng·ml -1 (3 σ ). Common co-existing ions, except Fe(Ⅲ), do not interfere with the determination. By masking Fe(Ⅲ) ion with NH 4F, the proposed method has been applied to the determination of copper in foodstuffs. RSD′s found are 2.0%~4.4% ( n =6). The catalytic and non-catalytic reaction are of pseudo-zero order, in the reaction time interval of 3.0~8.0min at 90°C. The apparent activation energies for the reactions are 103.8kJ·mol -1 and 156.1kJ·mol -1 respectively. The results obtained by the proposed method are in consistent with those obtained by the conventional DDTC extraction photometric method.更多还原