Feasibility of Identification and Monitoring of Arsenic Species in Soil and Sediment Samples by Coupled High-performance Liquid Chromatography — Inductively Coupled Plasma Mass Spectrometry

Abstract

The determination of four arsenic species (As^III, dimethylarsinic acid, monomethylarsonic acid and As^V) in soil and sediments following a single microwave extraction procedure was investigated using an on-line system involving high-performance liquid chromatography (HPLC) coupled with inductively coupled plasma mass spectrometry (ICP-MS). Phosphoric acid was used in conjunction with an open focused microwave system to extract arsenic compounds. This system was optimised with respect to acid concentration, microwave power and time in order to obtain the maximum rate of recovery whilst retaining the integrity of arsenic species. Using an anion-exchange column and buffered phosphate solution with methanol added as the mobile phase, good separation and sensitivity were achieved. Under these conditions, recoveries between 60 and 80% of the total As content were obtained, and the detection limits were in the range 1–2 mg kg^–1 for all species. The HPLC–ICP-MS system was used for the determination of arsenic species in acid extracts of in-house reference materials (soil and sediment samples from polluted areas). Only arsenate was found in soil but arsenite was the main species found in a polluted river sediment. Three certified reference materials were analysed to determine the concentrations of the four arsenic species, and the sum of the arsenic concentration was compared with the certified total arsenic value for each of the reference materials. This method allows the speciation of arsenic species in soil and sediment samples to be determined at natural levels, and enables their behaviour in the environment to be monitored.