Determination of chemical oxygen demand by a flow-injection method using cerium(IV) sulphate as oxidizing agent

A method based on flow injection was developed for the automated determination of chemical oxygen demand (COD) that provided a number of possibilities for improvement of the limitations of the standard manual methods. The strong oxidizing agent used is cerium(IV) sulphate, which resulted in a high degree of sample oxidation under mild operating conditions. The reaction between samples and cerium(IV) ion produced a sensitive and reproducible signal, i.e., a decrease in absorbance. The detection limit and relative standard deviation of the method were 0.5 mg l^-1 and 0.6% (n = 10), respectively, for a standard sample consisting of l-glutamic acid and lactose in a ratio of 5:1. When 50-μl samples were injected at a frequency of 20 h^-1, the determination range was 0.5-130 mg l^-1 COD. Chloride was tolerated up to a concentration of 30 g l^-1 without any masking agents. COD values for various types of wastewater samples correlated well with those obtained by standard manual methods.