Measurements of total lead concentrations and of lead isotope ratios in whole blood by use of inductively coupled plasma source mass spectrometry

Abstract

Methods are described for the accurate and precise determination of total lead and its isotopic composition in whole blood using inductively coupled plasma source mass spectrometry (ICP-MS). The sample preparation is a simple 1 + 24 dilution of blood (400 µl for total lead; 2000 µl for isotope ratios) using a diluent containing ammonia solution, (NH₄)₂H₂EDTA, NH₄H₂PO₄ and Triton X-100, which allows prolonged pneumatic aerosol generation without blockage of the Meinhard nebuliser. Sensitivities of up to 3 × 10⁶ counts s^–1 for ²⁰⁸Pb at a total lead concentration of 5 µmol l^–1(1 µg ml^–1) enabled total blood lead levels to be measured in 4 min per sample, with a detection limit of 0.072 µmol l^–1(15 µg l^–1). The agreement between ICP-MS and atomic absorption spectrometry (AAS) for this analysis was excellent: ICP-MS = 0.996 × AAS – 0.0165 µmol l^–1; r= 0.994. Isotope ratio measurements required 15 min to achieve the required accuracy and precision both of which were generally better than 0.5% for ²⁰⁶Pb : ²⁰⁷Pb and ²⁰⁸Pb : ²⁰⁶Pb isotopic lead ratios. The ICP-MS data for these ratios in ten quality control blood specimens had a mean bias relative to isotope dilution mass spectrometry of –0.412% for ²⁰⁶Pb : ²⁰⁷Pb ratios and of +0.055% for the ²⁰⁸Pb : ²⁰⁶Pb ratios. This level of accuracy and that of the total blood lead measurements is sufficient to permit application of these ICP-MS methods to environmental studies.