Trace levels of arsenic (As) in soil samples can be determined by conventional ICP-QMS with closed vessel digestion, but always suffer from interference of ions originating from the complicated matrix, mainly including 40Ca35Cl+, 40Ar35Cl+, 39K36Ar+, 150Nd2+, 150Eu2+ and 150Sm2+etc. In this study, 75As+, the mass for general detection, was effectively changed to 75As16O+ which could be detected at m/z 91 by reaction with oxygen in a Dynamic Reaction Cell (DRC). For the new interference of 91Zr+ on 75As16O+, boiling aqua regia extraction was used to remove most of the zirconium in the sample preparation procedure, and the residual 91Zr+ was oxidized to 91Zr16O+ by oxygen in the DRC. In addition, the signal intensity of 75As16O was improved 4-fold by addition of 4% methanol into the sample solution. The signal to background ratio (SBR) of As was obviously improved from 0.18 to 205 (the certified arsenic concentration is 1 μg L−1), and a limit of quantification (LOQ, 10σ) of 0.1 ng g−1 was obtained. The proposed method was successfully applied to analyze 20 soil samples collected from pig farms in livestock farming processes, and shows its great potential for trace As determination in environmental and geological samples.
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