Speciation analysis of arsenic in environmental solids Reference Materialsby high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry following orthophosphoric acid extraction

A method for the determination of arsenic species (arsenite, arsenate, mono methylarsonic acid (MMAA) and dimethylarsinic acid (DMAA)) in environmental solid samples has been studied and applied to three reference materials (r iver sediment, agricultural soil, sewage sludge) certified for their total As content and to real world samples. The analytical method used was ion-ex change liquid chromatography coupled on-line to atomic fluorescence spectro scopy 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, rangi ng from 0.02 to 0.04 mg (As) kg(-1) for all species in all matrices. This h igh sensitivity allows both the analysis of As-poor samples and the dilutio n of extracts, of As-rich ones, reducing, thus, the possibility of matrix i nterferences and allowing a drastic improvement of chromatograms obtained w hen 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, excell ent (90-100%) recoveries of total As being obtained for the sediment and th e sludge reference materials samples whereas yield did not exceed 62% for t he 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, MMA-A 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 t he presence of methylated species. On the whole, the method proposed has a very good potential as a routine sp eciation analysis procedure for As speciation studies in environmental soli ds. (C) 2001 Elsevier Science B.V. All rights reserved.