Abstract: A simple and precise method for direct determination of molar ratio of ²⁰⁶Pb/ ²⁰⁴Pb, ²⁰⁷Pb/ ²⁰⁴Pb and ²⁰⁸Pb/ ²⁰⁴Pb by ICP-MS was developed. The data acquirement parameters of MS for Quadrupole setting time(QST), Dwell time(DT), Integrated time and number of sweeps were investigated in detail. The relative standard deviation(RSD) of different Pb isotope ratios were less than 0.32%[n=5, ρ(Pb)=20 ng/mL]. The mass discrimination and dead time of detector was calibrated by using NIST981 solution. The mass bias factor(α) of ²⁰⁶Pb/ ²⁰⁴Pb, ²⁰⁷Pb/ ²⁰⁴Pb and ²⁰⁸Pb/ ²⁰⁴Pb were 0.002 5, 0.002 9 and 0.002 0, respectively. The dead time of detector was 7 ns. The proposed method has been applied to the analysis of geological standard reference materials containing AGV-1, BCR-2 and BHVO-2 .The relative error between this work and the recommend values or reported values was better than 0.73% and the relative standard deviation was better than 0.93%(n=5).

Key words: Inductively coupled plasma mass spectrometry(ICP-MS), Lead, Isotope ratio, Geological sample