The determination of the different forms of selenium in the environment is necessary owing to the different effects related to their respective chemical forms: species can either be considered as essential, e.g. Se(IV) is added to foodstuffs to care for selenium deficiency problems, or highly toxic, e.g. Se(VI) compounds. Techniques developed for the determination of Se(IV) and Se(VI) involve a succession of several analytical steps (e.g. reduction, separation, detection) which are often far from being validated. In addition, the knowledge related to the stability of the species is still very scarce. It was hence necessary to evaluate the state-of-the-art of Se-speciation analysis and the feasibility of preparing reference materials certified for their Se(IV) and Se(VI) contents.
The project aimed to evaluate the state-of-the-art of Se-speciation analysis and to certify reference materials of artificial freshwater for their contents of Se(IV) and Se(VI).
The feasibility study enabled to optimise storage procedures of artificial freshwater containing Se-species in such a way that an interlaboratory study was successfully concluded in 1995. The state-of-the-art was found to be good enough to perform a certification campaign and candidate CRMs were analysed by a group of laboratories, showing a good agreement among techniques and participants. Further stability checks carried out one year after the certification campaign have demonstrated, however, that instability of the Se-species over a long-term period was likely. While the original solutions stored in a polyethylene tank were found to be stable over 36 months, the solutions stored in 100 ml polypropylene bottles displayed losses of more than 20% of Se-species content which could not enable the materials to be accepted as CRMs. The results of the project are described in the Report EUR 18044 EN (1998).
The programme consisted in a feasibility study to optimise the storage procedures (type of containers, stability of species at different temperatures etc.) with respect to Se(IV) and Se(VI), the preparation of a limited batch of solution samples for an interlaboratory study, the organisation of an interlaboratory study with ca. 20 EU laboratories, the preparation of a large batch of two reference materials of artificial freshwater containing Se(IV) and Se(VI) and their subsequent certification.