恒电位电解法测定COD值准确性的影响因素分析

Influence Factors on the Accuracy of COD Values Measured by Potentiostat Electrolysis Method

在线水质监测亟需快速、准确的电化学COD传感器.以电化学沉积法制备的石墨基β-PbO2电极材料为工作电极时,其阳极响应电流强度Iresp与电解液中的有机物COD理论值之间呈良好的线性关系(R2>0.99),这是其作为COD电化学传感器的良好基础.然而,不同种类有机物的COD理论值(CODTh)与Iresp间的线性系数相差达1~2.3倍,该现象将影响真实水样的COD测定准确性.本研究通过电化学反应机理分析,认为扩散控制和电化学矿化反应控制二者之间的差异是造成不同种类有机物Iresp-CODTh线性斜率不同的主要原因.藉此,本研究建议在采用恒电位法测试COD值时,加强搅拌、增加电极表面吸附活性位点数量以及使用混合水样制作标线等方法提高测定准确性.

Rapid-responding and accurate electrochemical COD sensor is being developed for the demand of wastewater online detection. Using a graphite plate electrodeposited by β-PbO2 as anode, the anodic responding current intensity Iresp is well linear to the COD concentration of organics in the electrolyte （R2=0.99）, thus offering a possibility for the design of electrochemical COD sensor. However, the results show that the difference in chemical species caused the difference in the linear coefficient by 1 to 2.3 times, which would disturb the accuracy of COD analysis for authentic water samples. Based on the studies of electrochemical reaction mechanism, it is concluded that the deference in control by diffusion step or electrochemical mineralization step of those chemicals explain the difference in I resp-CODTh slope. Therefore, several methods are suggested to improve the accuracy of COD measurement through the anodic oxidation method.