Isotope ratio measurements using gas chromatography inductively coupled plasma mass spectrometry for the assessment of organolead sources

The measurement of isotope ratios (within individual species), for a range of organolead compounds, was carried out by coupling a capillary gas chroma tograph (HP 6890) to an inductively coupled plasma mass spectrometer (HP 45 00). Optimum conditions for the separation and detection of the derivatised lead organometallic compounds were studied focusing on the precise and acc urate measurement of isotope ratios on each chromatographic peak. Three lea d isotopes were monitored, 206, 207 and 208 using 66 ms integration time pe r isotope. Under optimum conditions adequate chromatographic peak profiles could be measured. Based on peak area ratios, isotope ratios were determine d for five butylated lead compounds (trimethyllead, dimethyllead, triethyll ead, diethyllead and inorganic lead) and mixed methyl-ethyl tetraalkyllead compounds from leaded gasoline. Mass bias was corrected using both ethylate d and butylated NIST 981 isotopic standard (Common Lead) and a certified en riched Pb-204 solution. No isotope fractionation effects were observed duri ng derivatisation of the different organometallic compounds. Applications o f this methodology include the differentiation between Pb sources of the di fferent standards used, the measurement of Pb isotope ratios in the organol ead compounds present in airborne particulate matter of Oviedo to ascertain their origin and the comparison with isotope ratios in the BCR CRM 605 urb an dust reference material. Significant differences between lead isotope ra tios in the different species of organolead compounds and in total lead (af ter acid digestion of the samples) were observed. These differences can be used to trace back sources of lead contamination, by resorting to the speci ation data, in cases where the isotope ratios of total lead in the samples are inconclusive in identifying Pb contamination sources.