DIRECT DETERMINATION OF LEAD IN GASOLINE USING EMULSIFICATION AND ARGON AND ARGON-OXYGEN INDUCTIVELY-COUPLED PLASMA-ATOMIC EMISSION-SPECTROMETRY

Lead in gasoline has been determined by emulsification and argon and a rgon-oxygen inductively coupled plasma atomic emission spectrometry (I CP AES). The intensity variations of inorganic and organic lead specie s in aqueous solution and in gasoline and decalin emulsions were studi ed using a sequential spectrometer. In an aqueous solution, Ph II 220. 35 nm intensities were higher than those observed in gasoline and deca lin emulsions. With normal aspiration conditions, Pb II intensities we re higher in the argon ICP than in the argon-oxygen plasma. However, u nder low pressure, Pb intensities were relatively higher with oxygen d oping, possibly due to enhanced pyrolysis of the solvent aerosol and v apour. The role of Y II 371.030 nm as an internal standard was evaluat ed. Lead II intensities mere 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 calibratio n curves, it compensated for differences in emulsion composition and f or 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 dete rmination of lead at the mg kg(-1) concentration level. The accuracy f or Ph determination in spiked gasoline emulsions and in NIST Pb in Fue l 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 s imilar to ICPs containing water only.