The current standard is equivalent to the application of ISO 6777-1984 “Water Quality-Determination of Nitrogen (Nitrite)- Molecular Spectrophotometric Method”. Based on the format of Chinese national standard, this standard has slight change and addition to the technical part of ISO 6777-1984. The current standard specifies spectrophotometric method to determine nitrogen (nitrite) in drinking water, groundwater, surface water and waste water.

Water quality-Determination of nitrogen (nitrite)-Spectrophotometric method  (GB 7493-87)