Results of an inter-laboratory analytical quality control programme for non-saline waters

Abstract

The Severn-Trent, South West, Welsh and Wessex Water Authorities have a statutory responsibility for the quality of water in the Severn Estuary. A Joint Committee was formed to coordinate the activities of the Authorities in respect of the management of the water quality, with special reference to the monitoring of polluting discharges entering the estuary. In order to carry out this duty effectively, comparability of analytical results between the laboratories of the four Authorities was considered to be essential and a Chemists' Sub-Committee was established to undertake this task. The Chemists' Sub-Committee was required to establish within a period of 3 years, and then to maintain, an inter-laboratory analytical quality control programme for a total of 17 determinands. It was found that even for relatively simple determinands such as ammonia, total oxidised nitrogen and chloride inter-laboratory comparability was not easy to achieve, and that once achieved, constant attention was necessary in order to maintain it. Hence the work required was much greater than at first envisaged and even so a perfect set of results was not possible for all determinands. This paper summarises the approach adopted, illustrates some of the problems experienced and presents results of the inter-laboratory comparability finally achieved.