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

The standard method for the determination of chemical oxygen demand (COD) with K 2 Cr 2 O 6 uses harmful chemicals, has a long analysis time, and cannot be used for on-site online monitoring. Therefore, it is 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 was dependent 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 is dependent on the ratio of the concentration of the hydroxyl radical and the organic species. We give an outlook on how to improve the method to increase the linear working range, avoid the signal variance and how to further explain the signal variance.