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

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 93Nb16O+, 92Zr16OH+ and 92Mo16OH+ on 109Ag+ were rapidly oxidized to higher oxides 93NbO2+, 92ZrO2H+/92ZrO2H+ and 92MoO2H+ by O2 as the reaction gas in DRC. However, interfering ions 89Y18O+ and 91Zr16O+ on 107Ag cannot be removed by this method, because the reaction rates of ZrO+ and YO+ to ZrO2+/ZrO3+ and YO2+/YO3+ were too low. Under the optimized O2 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.

Research highlights
► Ag determination is subject to serious Zr, Nb and Mo based interferences by ICP-MS.
► 93Nb16O+, 92Zr16OH+ and 92Mo16OH+ are eliminated by ion–molecule reactions in a DRC.
► Method is simpler, rapid, and does not require other expensive equipment or reagents.
► It has great potential for ultra-trace Ag determination in environmental samples.