Determination of Silver in Soil and Stream Sediments by ICP-MS/MS with Four Collision/Reaction Modes

BACKGROUND: It is difficult to accurately determine the content of Ag in soil and sediment due to the mass spectrum interference of niobium, zirconium oxide and hydroxide during inductively coupled plasma-mass spectrometry (ICP-MS) analysis.OBJECTIVES: To develop methods for the determination of trace Ag in soil and sediment samples by four collision/reaction modes.METHODS: The changes of mass spectrum signals of 93Nb16O+, 91Zr16OH2+, 92Zr16OH+ and 109Ag+ in helium, oxygen and ammonia were determined using inductively coupled plasma-tandem mass spectrometry (ICP-MS/MS). The interference elimination ability and elimination mechanism of different collision/reaction modes were investigated. The samples were digested by HCl-HNO3-HF-HClO4. The content of Ag in soil and stream sediments was determined by helium MS/MS mode, oxygen MS/MS mode, ammonia MS/MS mode and ammonia Mass-Shift mode.RESULTS: With the optimal gas flow rate in the tank of the four collision/reaction modes, the interference degree of niobium and zirconium on Ag were decreased more than 20, 1500, 1500 and 2000 times, respectively. The detection limits of the method were 0.005mg/kg, 0.002mg/kg, 0.003mg/kg and 0.003mg/kg, respectively. The accuracy and precision were verified by national reference materials of soil and sediment, while the relative errors of measured values and certified values were -1.4%-84.3%, -7.6%-7.2%, -15.0%-10.0% and -12.5%-8.6%, respectively. The relative standard deviations were 1.5%-6.3%, 1.4%-8.3%, 1.4%-5.9% and 0.7%-8.2%, respectively.CONCLUSIONS:Helium MS/MS mode has a low capacity to eliminate mass spectrometry interference, and is suitable for the determination of samples with little interference of niobium and zirconium. Oxygen MS/MS, ammonia MS/MS and ammonia Mass-Shift modes have a strong ability to eliminate mass spectrometry interference, which can be used for the determination of trace Ag in soil and stream sediments; and have the advantages of lower detection limit, wider linear range, and simultaneous determination of multiple elements, when compared with the industry standard DZ/T 0279.11-2016