Application of ultraviolet absorption spectroscopy for the determination of nitrogen compounds in anthropogenically impacted surface waters: A case study of the Kłodnica River

Abstract

Ultraviolet (UV) absorption spectroscopy is a rapid and reagent-free method for the determination of nitrogen compounds in surface waters; however, its application in anthropogenically impacted systems is limited by matrix interferences. This study evaluates the use of UVC spectroscopy for quantifying nitrogen compounds in the Kłodnica River, a watercourse strongly influenced by industrial and mining activities. Absorbance was measured at 220 nm, 235 nm, 254 nm, and 275 nm for ultrapure water, potassium nitrate reference solutions, and five river samples, both before and after filtration through a 0.45 µm membrane. Filtration enabled separation of light scattering caused by suspended particles, while multi-wavelength analysis was applied to compensate for natural organic matter interference. The results show that reliable quantification is achieved using wavelength pairs based on 220 nm, where absorbance of nitrogen compounds dominates over background effects. In contrast, measurements at 235 nm were strongly affected by matrix components, resulting in unstable correction and poor agreement with reference concentrations. Absorbance differences confirmed the influence of turbidity. A clear relationship between wavelengths enabled effective correction. The findings highlight the importance of wavelength selection and site-specific correction strategies for UV-based monitoring in complex, anthropogenically impacted waters.