Water quality - Determination of nitrogen - Manual method using oxidative digestion with peroxodisulfate and cadmium reduction

This document establishes a standardized procedure for determining nitrogen content in water samples. The method involves the oxidation and digestion of nitrate and nitrite using potassium persulfate under specific conditions, followed by the reduction of nitrate to nitrite via a cadmium column. The resulting nitrite is then quantified through spectrophotometric analysis at a defined wavelength, typically after reaction with specific reagents to form a colored azo compound. This manual approach ensures accurate measurement of total nitrogen species in various water matrices without relying on automated instrumentation. The protocol outlines detailed steps for reagent preparation, calibration curve construction, sample handling, and calculation of results to maintain consistency across different testing facilities. Adherence to these guidelines facilitates reliable data generation for environmental monitoring and compliance assessments. The procedure addresses potential interferences and provides specific quality control measures to verify the accuracy of the analytical process. By following this established method, laboratories can achieve comparable results when evaluating the nitrogen concentration levels in water sources.