Lead isotope determinations by inductively-coupled plasma mass spectrometry (ICP-MS): potential of sector field instruments

Abstract

Lead isotope measurements have been carried out using a high-resolution inductively-coupled plasma mass spectrometry (Finnigan MAT ELEMENT, configurated with CD-1 option) The method can be applied to all types of geological samples brought into solution form.Three common lead standards are used for documentation of the methos. Detection limits for 204Pb, 206Pb, 207Pb and 208Pb lie between 0.124 and 2.86 pg ml-1. Optimisation of scanning conditions at a count rate of approximately 200.000 cps for 206Pb and 207Pb, led to a relative standard deviation of 0.05% for the mean 207PPb and 207Pb, 206Pb isotope ratio, based on 15 consecutive measurements. The method can be routinely applied to gain geochronological and petrological data for genetic studies of mineral deposits, including deposits of industrial minerals. Because of space change effects in the skimmer cone region and mass-dependent sensitivity of the mass spectrometer, the measured intensity ratio of samples must generally be calibrated using external or internal standards of known isotope ratios to correct for mass blases and mass fractionation.