Operation of a proficiency testing scheme of trace elements in sewage sludge with reference values

A proficiency test (PT) was carried out to investigate the quality of labor atory results measuring trace elements in sewage sludge. The scheme relied on reference values, established through flame atomic absorption spectrosco py and instrumental neutron activation analysis. Within the framework of th e project, "Proficiency testing in Central and Eastern European Countries", the measurements were done in parallel using induced coupled plasma mass s pectrometry. This paper discusses the design of the PTS, the metrological c oncepts behind it and the way in which it was operated. The discussion incl udes the estimation of measurement uncertainty of the reference values obta ined, homogeneity testing and its uncertainty evaluation, as well as all re levant quality assurance aspects. From the results, it can be concluded tha t all measurement methods involved agree within their respective uncertaint ies. Furthermore, it can be concluded that it is feasible to operate a prof iciency test of trace elements in sewage sludge using reference values. The agreement between the reference values and the consensus values is satisfa ctory.