Heating and ultraviolet irradiation: Gas pressure meter-based analytical system for on-site and rapid monitoring of permanganate index (COD_Mn)

Permanganate index (COD_Mn) is one of the important indicators of surface water quality measurement. Herein, a portable analytical system was developed for on-site and rapid analysis of COD_Mn, organic substances in water were oxidized and transformed into gases, so that COD_Mn concentration was converted into a change of gas pressure signal, the pressure signal change was further detected by a gas pressure meter. Heating method and ultraviolet (UV) irradiation method were used as assisting technologies for oxidization of organic substances by acidic KMnO₄, a linear range of 2-150 mg l^-1 and a detectable limit of 2 mg l^-1 were obtained. Those methods were further applied to the detection of COD_Mn in various water samples (lake waters and domestic sewage) and certified reference water samples (BWZ 6974-2016C and BWZ 7617-2016), with recoveries of 89-111 %. Among them, a portable analytical system based on UV irradiation gas pressure meter was further established and used for the analysis of COD_Mn in field. It is a promising analytical system/device for COD_Mn monitoring in field, offering advantages of low-cost, easy-operation, portability and rapidness.