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.