Sensing of chemical oxygen demand (COD) by amperometric detection-dependence of current signal on concentration and type of organic species

The standard method to determine chemical oxygen demand (COD) with K2Cr2O6 uses harmful chemicals, has a long analysis time, and cannot be used for on-site online monitoring. It is therefore necessary to find a fast, cheap, and harmless alternative. The amperometric determination of COD on boron-doped diamond (BDD) electrodes is a promising approach. However, to be a suitable alternative, the electrochemical method must at least be able to determine the COD of water samples independently of the contained substances. Therefore, the current signal as a function of various organic materials was investigated for the first time. It was shown that the height of the signal current depended on the type of organic matter in single-substance solutions and that this substance dependency increases with the amount of COD. Those findings could be explained by the mechanism proposed for this reaction, showing that the selectivity of the reaction depends on the ratio of the concentration of hydroxyl radicals and organic species. We give an outlook on how to improve the method in order to increase the linear working range and avoid signal variance and how to further explain the signal variance.

Automated summary

The traditional method of COD determination using K2Cr2O6 is not suitable for on-site online monitoring due to the use of harmful chemicals and long analysis time. The amperometric determination of COD on BDD electrodes shows promise as a fast, cheap, and harmless alternative. This study investigates the relationship between current signal and various organic materials, revealing a substance dependency and its increase with COD amount. The findings are explained by the proposed reaction mechanism, which highlights the selectivity based on the concentration ratio of hydroxyl radicals and organic species.