Revisitation of mineralization modes for arsenic and selenium determinations in environmental samples

Mineralization procedures for arsenic and selenium analysis are usually lim ited to wet digestion methods owing to high volatility of these analytes, O n the other hand, variable amounts of silicon in some types of samples impl y elaborated mineralization procedures to liberate analytes which may be re tained in an insoluble residue. Consequently, methods for such material gen erally include an hydrofluoric step followed by an evaporation to dryness. This type of mineralization is most easily accomplished using a dry ashing procedure. For plant analysis, a well validated and readily applicable dry ashing method is used for a long time in several laboratories but up today one could suppose that As and Se determinations cannot be performed after s uch a type of mineralization. Surprisingly, it has been observed that for p lant samples these analytes are detected even after a calcination at 450 de greesC. The general usefulness of a dry ashing method for analysis of all o ther analytes (main, minor and trace elements) incitates us to also verify As and Se recoveries. Results obtained in this work indicate clearly that p lants of terrestrial origin may be mineralized using dry ashing procedure w ithout As and Se losses. This statement was confirmed by analyses of severa l reference terrestrial plant samples (RMs) and laboratory control samples. Another confirmation was given by the direct graphite furnace analysis of the same plant samples but in slurried form (SS-ETAAS). As a direct consequ ence, As and Se analysis in terrestrial plants no more necessitates a separ ate preparation methodology. On the other hand, significant losses of As an d Se were observed for aquatic plants, e.g. algaes. For the analysis of thi s type of samples, a separate wet digestion procedure remains unavoidable i f the determination of As and Se has to be considered. Also some preparatio n procedures were tested for As and Se-analysis of soil and sediment refere nce samples. In these cases the wet digestion with a mixture of nitric, per chloric and hydrofluoric acids seems to remain the best alternative. (C) 20 01 Elsevier Science B.V. All rights reserved.