Determination of Cd, Cu, Fe, Pb and Tl in gasoline as emulsion by electrothermal vaporization inductively coupled plasma mass spectrometry with analyte addition and isotope dilution calibration techniques

The presence of some elements can be undesirable in gasoline, not only by the possibility of damage of the motor parts and poor performance of the fuel, but also because of the pollution caused by the release of toxic metals to the atmosphere by the combustion of the fuel. The gasoline sample preparation as emulsion is an adequate method for the sample introduction for sensitive analytical methods. In this work, external calibration with aqueous standards, analyte addition and isotope dilution calibration techniques were employed for the determination of Cd, Cu, Fe, Pb and Tl in gasoline by electrothermal vaporization inductively coupled plasma mass spectrometry. The concentrations of Cu and Fe were additionally determined by electrothermal atomic absorption spectrometry. The ETV program for the analytes in a gasoline sample emulsion was optimized and the determination was carried out without modifier at 400 °C pyrolysis and 1900 °C vaporization temperatures. In these conditions, the external calibration against aqueous standards could not be applied for the analysis of gasoline as emulsion, since the results of recovery tests were not acceptable. The determination by analyte addition or isotope dilution employing these conditions could be carried out for Cd, Cu, Pb and Tl, but not for Fe. The use of 10 mg Pd in solution as chemical modifier allowed the determination of all studied analytes together, at 800 °C pyrolysis and 2100 °C vaporization temperatures. The limits of detection for the analytes in gasoline, by analyte addition or by isotope dilution, were better than 5 μg l−1. The measured concentrations for all analytes by analyte addition and by isotope dilution calibration techniques were mostly in agreement and the precision for both calibrations were also similar and adequate. Agreement was also found with concentration results for Fe and Cu obtained by ET AAS, without modifier.