Determination of lead and lead isotope ratios in gasoline by inductively coupled plasma mass spectrometry

Abstract

An accurate method for determining the concentration of lead in gasoline over the range 0.004–1500 µg g^–1 is described. Tetraalkyllead compounds in the gasoline are converted into water-soluble species that are subsequently extracted into dilute nitric acid. Lead concentrations in the nitric acid extracts are determined using inductively coupled plasma mass spectrometry with a bismuth internal standard. The relative standard deviation of this method is ±2.4% for lead concentrations greater than 0.1 µg g^–1. Studies with spiked samples and standard reference materials demonstrate excellent quantitative recoveries. The detection limit for lead in a 1 g gasoline sample is 0.004 µg g^–1. Gasoline samples as large as 25 g can be extracted to enhance the accuracy and precision of low level (–1) determinations. Isotope ratio measurements on National Institute of Standards and Technology Standard Reference Material 1636a (Lead in Reference Fuel) yield a ²⁰⁶Pb/²⁰⁷Pb ratio of 1.2230 ± 0.0035 (95% confidence interval). The precision of these ratio measurements is suitable for performing both isotope dilution analyses as well as isotopic tracer studies.