Optical Analysis Based on UV Absorption Spectrum for Monitoring Total Organic Carbon and Nitrate Nitrogen in River Water

The global deterioration of water quality due to climate change and industrialization has intensified the need for real-time monitoring systems. In South Korea’s automated water quality monitoring networks, measuring total organic carbon (TOC) and nitrate nitrogen (NO3-N) as a proxy for total nitrogen (TN) is critical; however, conventional analytical instruments face limitations such as high costs, long analysis times, and the need for chemical reagents. In this study, we developed and evaluated a simultaneous TOC and NO3-N measurement method using HASM-4000, a domestically developed optical sensor based on ultraviolet (UV) absorption spectroscopy. The sensor measures absorbance at 254 nm (TOC) and 220 nm (NO3-N) based on the Beer–Lambert law, with signal processing techniques including optical power compensation (OPC) and Binning–Interpolation (BinInterp) applied to enhance measurement accuracy. Calibration using standard solutions demonstrated excellent linear correlations (R2 > 0.99) between actual and estimated concentrations for both TOC and NO3-N, with accuracy and reproducibility validated against standard methods under laboratory conditions. However, performance degradation was observed in turbid mixed samples due to the optical limitations of the 10 mm pathlength, suggesting the need for future improvements such as adopting a 5 mm pathlength and upgrading optical components. The HASM-4000 sensor enables real-time measurement without a reagent, and preliminary testing with river water samples demonstrates its potential to advance Korea’s water quality monitoring infrastructure by reducing dependence on foreign technologies and facilitating network expansion with cost-effective domestic solutions.