Sequential Extraction Method for Speciation of Arsenate and Arsenite in Mineral Soils

摘要

A novel sequential extraction method for the speciationnof AsIII and AsV in oxic and anoxic mineral soils wasndeveloped and tested. The procedure consists ofnseven extraction steps targeting various As poolsnranging from weakly adsorbed to well-crystallinenspecies. Each step was specifically designed tonpreserve the AsIII and AsV redox states, e.g., byncomplexation of AsIII with diethyldithiocarbamate ornpyrrolidinedithiocarbamate, using mild reductiven(NH2OH· HCl) or oxidative (hot HNO3) extractions,nand complexing (Fe3+ with Cl-, acetate, and oxalate)nor precipitating (S2- with Hg2+) matrix elements,nwhich may cause As redox transformations. Usingnhigh-performance liquid chromatography-inductivelyncoupled plasma-mass spectrometry (HPLC-ICP-MS)nfor the quantification of dissolved AsIII and AsV innthe extracts, the detection limit for each step was innthe range of 1.0-75 ng As/g, depending on thenextraction matrix. Thus, the procedure is also wellsuitednfor As speciation in soils or sediments withnlow As concentrations, where analyses by X-raynabsorption spectroscopy (XAS) may be difficult. Thenentire extraction sequence can be performed undernnormal atmosphere, which greatly simplifies samplenhandling. The proposed method was tested usingnmodel minerals spiked with AsIII or AsV, two stronglynAs-polluted soil previously characterized for As speciationnby XAS, and three less-polluted soils.