Elimination of oxide interferences and determination of ultra-trace silver in soils by ICP-MS with ion–molecule reactions

Abstract

Silver is subject to significant spectral interferences caused by high concentrations of Zr, Nb, Mo and Y in inductively coupled plasma mass spectrometry (ICP-MS) analysis for soil or sediment samples. In this study, the Zr, Nb, and Mo based oxide and/or hydroxide polyatomic interferences were successfully eliminated by ion–molecule reactions in a dynamic reaction cell (DRC). These potentially interfering ions 93Nb 16O +, 92Zr 16OH + and 92Mo 16OH + on 109Ag + were rapidly oxidized to higher oxides 93NbO 2 +, 92ZrO 2H +/ 92ZrO 2H + and 92MoO 2H + by O 2 as the reaction gas in DRC. However, interfering ions 89Y 18O + and 91Zr 16O + on 107Ag cannot be removed by this method, because the reaction rates of ZrO + and YO + to ZrO 2 +/ZrO 3 + and YO 2 +/YO 3 + were too low. Under the optimized O 2 flow rate (2.4 mL min − 1 ) and DRC rejection parameter q (Rpq, 0.75), the background signal was reduced by up to 100-fold at m/z 109 and the limit of quantitation (LOQ, 10σ) for 109Ag was 0.5 ng g − 1 . The proposed method was used to determine the concentration of Ag in twenty-eight soil standard reference materials (SRMs). The accuracy of the results suggests that the method has great potential for the direct determination of trace or ultra-trace levels of Ag in various environmental samples.