DETERMINATION OF LEAD AND LEAD-ISOTOPE RATIOS IN GASOLINE BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY

An accurate method for determining the concentration of lead in gasoli ne over the range 0.004-1500 mug g-1 is described. Tetraalkyllead comp ounds in the gasoline are converted into water-soluble species that ar e subsequently extracted into dilute nitric acid. Lead concentrations in the nitric acid extracts are determined using inductively coupled p lasma mass spectrometry with a bismuth internal standard. The relative standard deviation of this method is +/-2.4% for lead concentrations greater than 0.1 mug g-1. Studies with spiked samples and standard ref erence materials demonstrate excellent quantitative recoveries. The de tection limit for lead in a 1 g gasoline sample is 0.004 mug g-1. Gaso line samples as large as 25 g can be extracted to enhance the accuracy and precision of low level (<0.1 mug g-1) determinations. Isotope rat io measurements on National Institute of Standards and Technology Stan dard Reference Material 1636a (Lead in Reference Fuel) yield a Pb-206/ Pb-207 ratio of 1.2230+/-0.0035 (95% confidence interval). The precisi on of these ratio measurements is suitable for performing both isotope dilution analyses as well as isotopic tracer studies.