Determination of Trace Silver in Geological Samples by Inductively Coupled Plasma-Mass Spectrometry with Acid Decomposition and Internal Standard Calibration

BACKGROUND Inductively coupled plasma-mass spectrometry (ICP-MS) is used for the determination of trace silver in geological samples. Hydroxides and oxides of Zr, Nb, Mo cause serious overlapping interference on the two mass numbers of 107Ag and 109Ag, which can result in a significant deviation of the results. OBJECTIVES To develop a method for precise determination of trace Ag in geological samples. METHODS Considering that the MS interference of 107Ag is relatively simple and only 90Zr16OH+ and 91Zr16O+ have interferences on 107Ag, 107Ag was selected for the determination of silver in ICP-MS analysis. In the sample pretreatment, hydrofluoric acid, perchloric acid and nitric acid were used for open digestion, and excessive ammonia was added to the extraction solution. The main interference element Zr of 107Ag was separated by precipitation. Trace silver was determined with Re as the internal standard to complement matrix effect and signal drift. RESULTS The content of trace silver in national standard materials of stream sediment, rock and soil was determined by ICP-MS. The test value was consistent with the certified value. The detection limit of the method was 0.0031μg/g, and the relative standard deviation (RSD) was 4.38%. CONCLUSIONS The method has the advantages of simple and accurate measurement of trace silver. Moreover, common metal elements can be determined before adding ammonia to the leaching solution, so that the extraction solution can be recycled.