Accuracy of determination of the electrical conductivity and the pH value of river waters: results of Water Authority tests made for the Harmonised Monitoring Scheme of the Department of the Environment

Abstract

The Department of the Environment, in collaboration with the Regional Water Authorities, has initiated a Scheme for the Harmonised Monitoring of Inland Fresh Waters in England and Wales. The Scottish Development Department has been closely associated with the development of this Scheme, and has introduced a similar scheme in Scotland in collaboration with the River Purification Boards. To achieve the required comparability of results, each of the 11 participating laboratories (drawn from 10 Regional Water Authorities and 1 River Purification Board) takes part in an analytical quality control (AQC) programme; this work is coordinated by the Water Research Centre. The general approach adopted to AQC has already been described, and this paper presents the results of tests made on the determination of pH value and electrical conductivity in river waters. The accuracy requirements for both determinands (that the total error on a single result should be not larger than 0.2 unit, for pH, and not larger than 20% of sample conductivity or 5 µS cm^–1, whichever is the greater, for conductivity) were essentially achieved by all 11 participating laboratories. Inter-laboratory tests on the determination of pH were, however, restricted to the distribution of buffer solutions because river samples examined were not sufficiently stable.