Direct determination of lead in gasoline using emulsification and argon and argon–oxygen inductively coupled plasma atomic emission spectrometry

Abstract

Lead in gasoline has been determined by emulsification and argon and argon–oxygen inductively coupled plasma atomic emission spectrometry (ICP AES). The intensity variations of inorganic and organic lead species in aqueous solution and in gasoline and decalin emulsions were studied using a sequential spectrometer. In an aqueous solution, Pb II 220.35 nm intensities were higher than those observed in gasoline and decalin emulsions. With normal aspiration conditions, Pb II intensities were higher in the argon ICP than in the argon–oxygen plasma. However, under low pressure, Pb intensities were relatively higher with oxygen doping, possibly due to enhanced pyrolysis of the solvent aerosol and vapour. The role of Y II 371.030 nm as an internal standard was evaluated. Lead II intensities were similar to those of Y II when decalin and gasoline contents in the emulsion and nebulization conditions varied. Although Y II did not improve the internal accuracy of the calibration curves, it compensated for differences in emulsion composition and for long- and shortterm variations. Although detection limits of Pb in gasoline emulsions were significantly degraded relative to an aqueous solution and a decalin emulsion, they are adequate for the direct determination of lead at the mg kg–1 concentration level. The accuracy for Pb determination in spiked gasoline emulsions and in NIST Pb in Fuel standard reference samples was satisfactory when iodine and Aliquat 336 (Tricapryl methyl ammonium chloride) were added to convert labile Pb species. The Mg II/Mg I ratio was used as a practical criterion of the robustness of the plasma and indicated that emulsion plasmas are similar to ICPs containing water only.