有机物种类对恒电位电解法测定COD值准确性的影响

以β-PbO2/石墨电极为工作电极,在支持电解溶液中加入一定量待测有机物,在低于析氧电位下进行恒电位电解时,因电极表面吸附态羟基自由基的消耗速率受电解质溶液中有机物分子向电极表面的扩散过程控制,表现为阳极电流强度的增加值(ΔI)与有机物质量浓度ρ之间呈线性关系。本文研究了多种待测有机物的ΔI与ρ的线性关系,发现由于有机物种类不同造成羟基自由基消耗速率不同,因而线性比例系数有所不同。实验结果表明在测定混合水样的化学需氧量(COD)值时,应采用与待测水样具有相似有机物混合比例的标准溶液制作工作曲线,以减少测量误差。

The effect of chemical species on the accuracy of COD values measured by constant potential electrolysis method

When the organic matter in aqueous solution is electrolyzed at constant potential using a β-PbO2/graphite electrode as the working anode, the reaction rate between organic molecules and adsorbed hydroxyl radicals is controlled by the diffusion of the organic molecules towards to the surface of the electrode. For fined stirring rate and viscosity, the variation in anodic current has a linear relationship with the concentration of organic matter in water. Different kinds of chemical species were tested in this study. Although each chemical species displayed a good linear relationship, the proportionality coefficients were different due to the different diffusion coefficients. Therefore, when a sample containing a mixture of chemical species is tested, a calibration curve should be made based on standard solutions with similar proportions of these chemicals.