Determination of ammonia and Kjeldahl nitrogen by indophenol method

Abstract

The Berthelot reaction, based on development of a deep blue colour when ammonia reacts with phenol and alkaline hypochlorite, was investigated and modified. The reaction variables were studied, and a convenient and reliable analytical procedure was developed for ammonia and Kjeldahl nitrogen determination, well suited for routine analysis of fresh and waste water. The buffering system introduced into the reagents permits examination of domestic wastewater, without pH correction, in the 3–11·5 range. The method gives highly reproducible results in the range of 0.02–1 mg l−1 ammonia nitrogen (1 cm light path). The solutions are ready for photometric measurement after 45 min of colour development at room temperature, and remain stable at least 48 h.Interfering substances likely to be present in domestic wastewater are hardness above 400 mg l−1 and nitrite ions above 5 mg l−1n. In high-ammonia wastewater samples, this interference is eliminated by the dilution required for photometric measurements.