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

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 ((WO+)-W-202) was drastically oxidized to higher oxide ions ((WO2+)-W-218 or (WO3+)-W-234) by O-2 as the reaction gas in the DRC, while the analyte ion (Hg-202(+)) cannot react with O-2. Under the optimized O-2 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, 10 sigma) for Hg-202 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.