Rapid, sensitive and on-line measurement of chemical oxygen demand by novel optical method based on UV photolysis and chemiluminescence

A novel on-line method based on the combination of UV photolysis and chemiluminescence detection was established and experimentally validated for the determination of chemical oxygen demand (COD). A quantitative amount of free radicals can be produced by analytes in the UV irradiation process. By utilizing the phenomenon that luminol can be oxidized by the free radicals to produce luminescence, COD was successfully determined indirectly. This new approach overcomes many problems associated with the conventional COD determination techniques such as long analysis time, tedious operations, consumption of expressive and toxic reagents, production of secondary toxic waste and poor reproducibility. The method was successfully applied to the determination of COD in synthetic samples, certified reference samples and real samples of river water and lake water. A limit of detection of 0.08 mg/L COD with a linear dynamic range of 0.2–20 mg/L was achieved under the optimum experimental conditions. The proposed method is a unique method that is environmentally friendly (without using any strong oxidizing reagent and any catalysts such as titanium dioxide), rapid (with only 5–10 min required for each sample), sensitive (with the lowest limit of detection for COD so far), simple (mainly with a photo-reactor and a chemiluminescence detector) and automated (using an intermittent flow system).