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

摘要

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 ~(93)NbO_2~+~(92)ZrO_2H~+and ~(93)Zr~(16)0H~+and ~(92)Mo~(16)OH~+ on ~(109)Ag~+ were rapidly oxidized to higher oxides ~(93)NbO_23~+,~(92)ZrO_2H~+/~(92)ZrO_2H~+ and~(92)MoO_2H~+ by O_2 as the reaction gas in DRC. However, interfering ions ~(89)Y~(18)O~+ and ~(91)Zr~(16)0~+ on ~(107)Ag cannot be removed by this method, because the reaction rates of ZrO~+ and YO~+ to ZrO_2~+/ZrO_3~+ and YO_2~+/VO_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, 10a) for 109Ag was 0.5 ngg~(-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.