Improved lead isotope ratio measurements in environmental and biological samples with a double focussing magnetic sector inductively coupled plasma mass spectrometer (ICP-MS)

Abstract

A method to measure lead (Pb) isotope ratios in biological and environmental samples using a single collector double focussing magnetic sector inductively coupled plasma mass spectrometer (ICP-MS) is presented. This method is intercalibrated with multicollector thermal ionization mass spectrometry (TIMS) to assess the suitability of the ICP-MS method for accurately and precisely identifying sources of environmental Pb exposure to humans. Results indicate that the external measurement precision (reproducibility) of this method, as evaluated by repeated analyses of the Pb isotope standard NBS 981 over the course of a year, was <0.1% (1&sigma;) for ²⁰⁶ Pb: ²⁰⁴ Pb, ²⁰⁷ Pb: ²⁰⁶ Pb and ²⁰⁸ Pb: ²⁰⁶ Pb ratios. Accuracy of isotope ratio measurements by ICP-MS was evaluated by comparing analyses of whole blood (biological) and household dust (environmental) samples with the definitive TIMS analyses of the same samples. For whole blood and dust samples, the ²⁰⁶ Pb: ²⁰⁴ Pb, ²⁰⁷ Pb: ²⁰⁶ Pb and ²⁰⁸ Pb: ²⁰⁶ Pb ratios measured by ICP-MS and TIMS generally agreed to within twice the propagated standard deviation (2&sigma;, &sigma;=√&sigma;TIMS2+&sigma;ICP-MS2)of both methods. However, a small but systematic difference between the Pb isotope ratios of blood measured with the two methods was apparent. The source of this difference remains under investigation. These data demonstrate that this ICP-MS method provides improved accuracy and precision of lead isotope ratio measurements compared to previous ICP-MS methods, and is suitable for use in studies to evaluate sources of environmental Pb exposure to children. Further, the increased samplethroughput and reduced cost of analyses using this method are substantial advantages over the more time-consuming and expensive TIMS method. Consequently, this Pb isotope methodology should prove useful as a routine tool in the investigation and mitigation of Pb exposure associated hazards.