This work focuses on the experimental optimisation of a newly developed photoelectrochemical system for the determination of chemical oxygen demand (PECOD). This method is developed based on a photoelectrochemical degradation principle. Chemical oxygen demand (COD) is directly quantified by measuring the amount of electron transferred at a TiO2 nanoporous thin-film electrode during an exhaustive photoelectrocatalytic degradation process in a thin-layer photoelectrochemical cell. In this fashion, the COD value of a sample can be determined in a simple, rapid and accurate manner. The PECOD is a direct and absolute method that requires no calibration. The effects of important experimental conditions, such as light intensity, applied potential bias, supporting electrolyte concentration and oxygen concentration, on analytical performance have been investigated and optimum experimental conditions were obtained. Analytical linear range of 0360 ppm COD with a practical detection limit of 0.2 ppm COD were achieved. Real sample analyses were also carried out. The results demonstrated that the measured COD values using the PECOD and the standard methods were in an excellent agreement.