A photocatalytic oxidation method for the detection of the chemical oxygen demand (COD) of the ground water using sol-gel-based nano-TiO₂ film, which was coated onto the quartz tube, was proposed. In this method, the photo-exited conduction band electrons released from illuminated nano-TiO₂ film could be easily accepted by Ce(IV) to enhance the activity of photocatalytic degradation of organic compounds. Therefore, the COD of a given sample can be assessed by determination of the change of the concentration of Ce(IV). Under the optimum operation conditions, the determination range of COD was 1.0～12 mg•L^－1 and the limit of detection was 0.4 mg•L^－1. This method was also applied to the determination of the COD of ground water samples. The results were in good agreement with those from the conventional (i.e., permanganate) COD methods.

Key words: chemical oxygen demand, photocatalytic oxidation, nano-TiO₂ film, Ce(IV)