Radioanalytical Methods: Data Quality, Method Validation and Use of Standard Reference Materi~ls VALIDATION OF METHODS FOR THE DETERMINATION OF ALUMINIUM IN FISH GILLS BY INAA AND ICP-MS

In a European study of fish death in mixing zones of rivers with different acidifies a reliable determination of A1 and other elements in gills from freshwater fish was required, and both INAA and ICP-MS were studied as candidate reference methods. INAA requires minimum sample handling with a correspondingly small risk of contamination and no blank value; however, a careful study was needed of both nuclear interference from P and the increased detection limit caused by other major elements in the sample, before reliable results for A1 could be ascertained. ICP-MS requires dissolution of the sample with a resulting risk of contamination and a significant reagent blank; while sensitivity was good, the interference from N created problems for sample decomposition in the microwave oven. Our experience with actual samples indicates that both methods suffer from considerable contamination problems, requiring that samples be handled in a clean bench with superpure reagents. Nuclear interference was determined experimentally by irradiating stoichiometric P-compounds with and without a Cd-shield; the observed interference of 1 Ilg AI from 50 mg of P was found to require no correction in almost all cases. The accuracy of results was ascertained by analyzing SRM 1577 Bovine Liver. Concentrations of several trace elements in lakes and rivers in the Scandinavian countries have been found to increase as a result of acid precipitation associated with the combustion of fossil fuels. Higher levels of aluminium in particular may be causing fish death in mixing zones of rivers with different acidity, 1, and this has initiated a European Community project under the STEP programme to study this effect. It was decided to carry out 'trace multielement analysis of fresh water and fish by inductively coupled plasma mass spectrometry (ICP-MS), permitting direct determination of up to 49 elements 2 including A1. As a quality control, a fraction of the fish samples were also analyzed by instrumental neutron activation analysis (INAA). Verification of results by ICP-MS is therefore based on the validation of the 1NAA method, which was carried out with sPecial reference to the determination of aluminium in fish g~l!s.