Rapid Determination of Chemical Oxygen Demand in Environmental Water Samples by Merging Zone Stop-Flow Injection Spectrophotometry

A method is proposed for the determination of chemical oxygen demand (COD) in environmental water samples with merging zone stopflow injection spectrophotometry in KMnO4 system. The determination condition was optimized with temperature of 70℃, pump speed of 1.5 mL/min, stopflow time of 60 s, sampling volume of 300 μL, reagent volume of 150 μL, KMnO4 concentration and acidity of 0.08 mol/L and 1.0 mol/L respectively, the acidity of the carrying liquid (H2SO4） of 10 mol/L and analytical frequency of 30 samples per hour. Up to 10000 mg/L of Cl–does not interfere on the determination. The detection limit of the method is 1 mg/Lwith dynamic linear range of 3~150 mg/L for COD. The precision of the method is 12%RSD (n＝7) for the sample with 50 mg/L of COD. The method has been applied to the determination of COD in river, pool and surface water samples and the results are in agreement with those obtained by traditional potassium dichromate method