Direct Determination of Ag in Geological Samples by Membrane Desolvation-Inductively Coupled Plasma-Mass Spectrometer

A method for direct determination of Ag in geological samples has been developed. In this study, various conditions involving optimizing the operating parameters of inductively coupled plasma-mass spectrometer (ICP-MS) with or without membrane desolvation system were investigated. In comparison to the cooling spray chamber, the interferences of 91Zr16O+, 91Zr18O+, 90Zr16OH+, and 90Zr18OH+ were found to be reduced by three orders of magnitude using membrane desolvation sample introduction system. The addition of 8 ml min−1 nitrogen to the carrier gas flow rate in membrane desolvation-ICP-MS increases sensitivity for Ag by a factor of 3.5, and reduces the oxide and hydroxide interferences by approximately 50%. Under the optimum conditions, the detection limit of Ag was 0.0005 µg l−1. The excellent agreement between the determination Ag concentration values (r = 0.995) in various geological samples (n = 103) by using isotopes of 107Ag and 109Ag indicates negligible contributions of polyatomic interferences produced by Zr, Nb, and Y at these m/z. The proposed method was successfully applied to the direct determination of Ag in a series of international geological reference materials.