Development and application of a HPIC-ICP-MS method for the redox arsenic speciation in river sediment pore waters

Abstract

A new sensitive chromatographic method has been developed for As speciation determination in anoxic pore waters. Starting from aliquots of 25 μL, the different As species As(III), As(V), MMAA^V and DMAA^V were separated in less than 4 min by HPIC-ICP-MS using the IonPac® AG7-AS7 anion-exchange column set and dilute HNO₃ as mobile phase. The detection limits were below or equal to 0.25 μg L⁻¹ for each As species, which makes the method efficient to determine As speciation in poorly-contaminated sediments. In addition, no precipitation of iron and manganese (hydr)-oxides was observed since the anoxic samples were systematically carefully manipulated under nitrogen atmosphere. Chlorides were eliminated by the chromatographic separation, thus making possible speciation analysis in estuarine or seawater samples. The use of internal standard was not necessary due to good signal stability (<10%) at m/z 75 over 4 h of analysis. An environmental application has also been successfully performed in the Marque River (Northern France). Inorganic As species were detected in pore waters at low concentrations [below 1 and 10 μg L⁻¹, for As(V) and As(III) respectively]. Others As species, identified as thioarsenic species, were also detected.