Speciation of inorganic arsenic in particulate matter by combining HPLC/ICP-MS and XANES analyses

Abstract

Inorganic arsenic species in ambient particulate matter (PM₁₀ and PM_2.5) have been determined in an urban area, in the vicinity of a metallurgical industrial plant. The developed high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC/ICP-MS) method allows monitoring of particulate As(III) and As(V)-species, with a limit of quantification of 0.34 ng m⁻³ As(III) and 0.23 ng m⁻³ As(V), respectively. Good agreement was obtained between the sum of the concentrations of As(III) and As(V) determined by HPLC/ICP-MS and the total As concentrations determined by XRF, indicating a complete extraction of the As species. During the measuring campaigns for PM₁₀ and PM_2.5, a significant conversion (oxidation) up to 54% of exogenous spiked As(III) was observed. The total amount of the spiked As(III) was well-recovered (PM₁₀ and PM_2.5 on average 108% and 101%, respectively). The extraction of the filter in combination with the sampled air matrix is likely to induce the As(III) conversion. The average measured As concentration in PM₁₀ during a 40-day monitoring campaign (30 ng m⁻³) at a hot spot location is above the European target value of 6 ng m⁻³. The measured As concentration in PM_2.5 was half the value of the measured concentration in PM₁₀ and no relative enrichment of total As was observed in either particulate matter fractions. However, in PM₁₀, As(V) was the main component, while in PM_2.5, As(III) was the dominant species. During the monitoring campaign, the fraction of particulate As(III) varied between 19 and 61% in PM₁₀ and a trend towards a higher fraction of As(III) with increasing concentration of total As was observed. XANES and XRD analyses were used for the identification of arsenic species in local PM sources and confirmed the presence of Ca₃Sr₂(AsO₄)_2.5(PO₄)_0.5(OH), As₂O₃ and As₂O₅ species.