Accuracy of determination of total oxidised nitrogen and nitrite in river waters: Analytical Quality Control in the Harmonised Monitoring Scheme

Abstract

The Department of the Environment, in collaboration with the Regional Water Authorities, has initiated a Scheme for the Harmonised Monitoring of the Quality of Inland Fresh Waters in England and Wales. The Scottish Development Department has introduced a similar scheme in Scotland in collaboration with the River Purification Boards. To achieve the required comparability of results from all laboratories involved, each laboratory takes part in an analytical quality control (AQC) scheme; this work is co-ordinated by the Water Research Centre. The general approach adopted to AQC has been described, and this paper presents the tests made and results obtained in the determination of total oxidised nitrogen and nitrite in river waters. Broadly, each of the 11 participating laboratories achieved total errors of not greater than ±20% of the determinand concentration or 0.1 mg l^–1 of nitrogen (whichever was the larger for different sample concentrations).