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).
