A modified sequential extraction method for arsenic fractionation in sediments.

A modified sequential extraction method was developed to characterize arsenic (As) associated with different solid constituents in surficial deposits (sediments), which are unconsolidated glacial deposits overlying bedrock. Current sequential extraction methods produce a significant amount of unresolved As in the residual fraction, but our proposed scheme can fractionate >90% of the As present in sediments. Sediment samples containing different As concentrations (3-35 μg g(-1)) were used to assess the developed method. The pooled amount of As recovered from all the fractions using the developed method was similar (83-122%) to the total As extracted by acid digestion. The concentrations of As in different fractions using the developed scheme were comparable (89-106%) to the As fractions obtained by other existing methods. The developed method was also evaluated for the sequential extraction of other metals such as copper (Cu), cobalt (Co), chromium (Cr) and strontium (Sr) in the sediment samples. The pooled concentrations of these four individual metals from all the fractions were similar (96-104%) to their total concentrations extracted by acid digestion. During method development, we used extractants that did not contain chloride to eliminate formation of polyatomic ions of argon chloride ((40)Ar(35)Cl) that interfered with (75)As when analyzed using inductively coupled plasma mass spectrometer (ICP-MS). The results suggest that the developed method can reliably be employed for complete As and other metals' fractionation in sediments using ICP-MS.