Improvement of the Method for Determining Total Nitrogen in Water Quality Using Alkaline Potassium Persulfate Ultraviolet Spectrophotometry

Alkaline potassium persulfate (K₂S₂O₈) ultraviolet (UV) spectrophotometry is the routine method to analyze total nitrogen (TN) in water and is important for studying pollutants in water and the geochemical cycling of TN. However, several analytical conditions can influence the accuracy of the results. (1) The blank, purity, and storage time of K₂S₂O₈. For example, a blank UV of K₂S₂O₈ exceeding 0.030 can lead to a significant underestimation of results. (2) The digestion method of bundling colorimetric tubes in high temperature and high pressure is time-consuming. (3) Improper sample storage conditions can lower measurement results. To improve the accuracy and efficiency of TN measurement in water samples, this study compared the storage times of different K₂S₂O₈, different digestion methods, and sample storage methods. The results show that the domestic premium-grade alkaline K₂S₂O₈ should be stored for <30 days (blank UV<0.03). The insertion digestion method is much more efficient (124°C, 20min). Acidification extends samples’ shelf life from 1 day to 7 days. Therefore, choosing domestic premium-grade K₂S₂O₈ and using the modified insertion method for sample digestion results in lower detection limits, higher digestion efficiency, minimal risk of contamination and misplacement, and improved accuracy of TN measurement in water quality analysis.