An online segmented continuous flow analysis system for rapid determining chemical oxygen demand in seawater to assess organic pollution levels

By integrating ultraviolet (UV) photocatalytic oxidation digestion with segmented continuous flow analysis technology, an online measurement method and analysis system for the alkaline chemical oxygen demand (CODMn) in seawater, based on the color-change reaction of potassium permanganate, has been established. This represents the first application of UV photocatalytic oxidation technology in the measurement of CODMn in seawater. The system effectively overcomes the limitations of high-temperature and high-pressure digestion methods employed in traditional CODMn analysis. The detection limit was 0.13 mg/L, the linear range was 0.00 mg/L ~ 4.60 mg/L, with a relative standard deviation of 2.30 % (n = 11), and recovery rates of 95.33 % ~ 109.50 %. Additionally, the system minimized interference from salinity, making it suitable for CODMn determination in seawater. Compared to the national standard method, the maximum average relative error was 0.042, lower than the conventional standard of 0.10, indicating high accuracy. The analysis of seawater samples from the Yangma Island area further confirmed the reliability of the system in practical testing and regional organic pollution assessment. The system demonstrated excellent anti-interference capabilities, rapid detection speed, and ease of operation, providing significant application potential in seawater CODMn measurement.