Application of ion molecule reaction to eliminate WO interference on mercury determination in soil and sediment samples by ICP-MS

Abstract

Mercury is subject to severe tungsten oxide (WO) interference in the direct ICP-MS analysis for soil or sediment samples. In this study, a method based on ion molecule reaction (IMR) was used to eliminate the WO spectral interference in a dynamic reaction cell (DRC). Interfered ion (²⁰²WO⁺) was drastically oxidized to higher oxide ions (²¹⁸WO₂⁺ or ²³⁴WO₃⁺) by O₂ as the reaction gas in the DRC, while the analyte ion (²⁰²Hg⁺) cannot react with O₂. Under the optimized O₂ flow rate (1.9 mL min⁻¹) and DRC rejection parameter q (Rpq, 0.80), the background signal was reduced by up to 1000-fold at m/z 202 and the limit of quantitation (LOQ, 10σ) for ²⁰²Hg was 1 ng g⁻¹. The proposed method was applied to direct determination of Hg in a series of soil and sediment standard reference materials (SRMs) and the satisfactory results indicate that it has great potential for the determination of trace or ultra-trace level mercury in various environmental or geological samples.