Speciation analysis of arsenic in environmental solids Reference Materials by high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry following orthophosphoric acid extraction
Résumé
A method for the determination of arsenic species (arsenite, arsenate, monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA)) in environmental solid samples has been studied and applied to three reference materials (river sediment, agricultural soil, sewage sludge) certified for their total As content and to real world samples. The analytical method used was ion-exchange liquid chromatography coupled on-line to atomic fluorescence spectroscopy through hydride generation. It was applied to the determination of As species in orthophosphoric acid extracts of the solids; the efficiency of this extraction procedure was studied in details, as well as the stability of extracts of As-rich ones. Very low detection limits were obtained, ranging from 0.02 to 0.04 mg (As) kg-1 for all species in all matrices. This high sensitivity allows both the analysis of As-poor samples and the dilution of extracts, of As-rich ones, reducing, thus, the possibility of matrix interferences and allowing a drastic improvement of chromatograms obtained when high concentrations of extractant are used. The efficiency of orthophosphoric acid extraction was shown to depend more upon the nature of the material analysed than on acid concentration, excellent (90-100%) recoveries of total As being obtained for the sediment and the sludge reference materials samples whereas yield did not exceed 62% for the soil Reference Materials. Procedures allowing a convenient stability of As species, including As(III), in the extracts are presented. In the three Reference Materials studied As(V) was found to be the main species, As(III) being only a minor component except in sludge where it amounts to ca. one-third of total As; methylated species, MMAA and DMAA, were evidenced only in the sludge sample at low (0.2-0.3 mg (As) kg-1) concentrations. Some applications to "real world" untreated equatorial sediment or agricultural soil samples evidenced similar abundances of As(V) and As(III) as well as the presence of methylated species. On the whole, the method proposed has a very good potential as a routine speciation analysis procedure for As speciation studies in environmental solids. © 2001 Elsevier Science B.V. All rights reserved.