Determination of Chemical Oxygen Demand in Water Samples Using Gas-phase Molecular Absorption Spectrometry

Chemical oxygen demand (COD) is important for water quality assessment as it represents the level of reductive organic pollution from eutrophication in aquatic systems. For surface water quality monitoring, permanganate is usually applied as an oxidizing reagent, and the routine COD_Mn determination is mostly achieved by titration method. However, this titration method is tedious and time consuming, and the results suffer from environmental temperature fluctuations and complicated operation techniques. In this study, a novel COD_Mn determination method was developed using gas-phase molecular absorption spectrometry equipped with an online automated digestion device for the first time. The effects of digestion temperature, digestion time and sulfuric acid content were thoroughly studied. This method exhibited good linearity (0.35 to 12 mg/L), a low detection limit (0.12 mg/L), and good RSD from various water samples (0.71 - 2.37%). When used for COD_Mn determination in routine water quality monitoring, this automated GPMAS can considerably improve analysis speed, efficiency, accuracy and stability compared to the traditional titration method.