Lead isotope ratio measurements by ICP-MS: Accuracy, precision, and long-term drift

The application of inductively coupled plasma mass spectrometry (ICP-MS) for the direct, routine determination of Pb isotope ratios was investigated. Short-term precision of the measurements was 0.2 to 0.3% - Long-term precision, covering a period of four months, was nearly as good. The Pb isotope ratio measurements were corrected for the mass discrimination factor by using NIST SRM-981 (Common Pb Isotopic Standard). More than 30 soil samples were analyzed for ²⁰⁶Pb/²⁰⁷Pb using this method. The results were compared with those of thermal ionization mass spectrometry (TLMS). The ICP-MS results of all samples agree with the TIMS results within a relative standard deviation of 0.5%, and except for two samples, all agree even within a relative standard deviation of 0.3%.