Lead isotope ratio analysis of bullet samples by using quadrupole ICP-MS

The measurement conditions for the precise analysis of the lead stable isotope ratio by using an ICP-MS equipped with a quadrupole mass spectrometer were studied in order to apply the technique to the forensic identification of bullet samples. The values of the relative standard deviation obtained for the ratio of Pb-208/Ph-206, Pb-207/Pb-206 and Pb-204/Pb-206 were lower than 0.2% after optimization of the analytical conditions, including the optimum lead concentration of the sample solution to be about 70 ppb and an integration time for I m/z of 15 s. This method was applied to an analysis of lead in bullets for rifles and handguns; a stable isotope ratio of lead was found to be suitable for the identification of bullets. This study has demonstrated that the lead isotope ratio measured by using a quadrupole ICP-MS was useful for a practical analysis of bullet samples in forensic science.