Determination of Silver in Regional Geochemical Samples by Inductively Coupled Plasma-Mass Spectrometry with Mixed Acids Digestion

There exists much error during determination of trace silver in geochemical samples by traditional inductively coupled plasma-mass spectrometry (ICP-MS) due to the interference of zirconium (Zr) and niobium (Nb) oxides. To eliminate the disturbance, a simple and accurate method combining mixed acid digestion and ICP-MS was built, in which the effect of He flow rate under kinetic energy discrimination (KED) mode was also investigated. Specifically, the samples were firstly digested by mixed nitric-hydrofluoric-perchloric acids. Then, the internal standard ¹⁰³Rh was added into the test sample after nitrohydrochloric acid extraction to correct matrix interference and instrument signal drift. To further eliminate the interference of Zr and Nb oxides on Ag, the He flow of the collision pool was increased to 7.0mL/min, thus significantly reducing the mass spectrum interference of silver without deterioration of the signal-background ratio. Verified by national first grade reference materials, the analysis results were within the allowable range of the standard value. The detection limit (3SD) of the method was 0.005g/g with the relative standard deviation of 1.43%−11.22% (n=12). This method is suitable for the analysis of silver in regional geochemical samples such as soil, stream sediments and rocks.