Combination of extraction induced by microemulsion-breaking and pre-concentration using magnetic nanoparticles for multi-element determination of Cd, Cr, Cu and Pb in gasoline samples using energy dispersive X-ray fluorescence spectrometry

The combination of the extraction induced by microemulsion-breaking (EIMB) and preconcentration using the solid-phase extraction (SPE) using magnetic nanoparticles (MNP) for determination of Cd, Cr, Cu and Pb in gasoline samples by energy dispersive X-ray fluorescence spectrometry (EDXRF) is proposed. The procedure was based in the formation of a three components microemulsion: gasoline as organic phase, n-propyl alcohol as an emulsifier and 0.01 mol L-1 HNO3 as aqueous phase. After formation of the microemulsion, Iris/nitric acid buffer (0.1 mol L-1, pH 8.5) was used for the microemulsion breaking and adjust the pH simultaneously. Subsequently, an amount of CoFe2O4 nanoferrite was added to the medium for the retention and preconcentration of the species of interest present in the aqueous phase of the broken emulsion. After a contact time between the nanoparticle and the mixture, the solid phase was separated from the supernatant with the aid of a magnet and, after drying, the determination of the analytes was performed directly on the solid support (nanoferrite) by EDXRF. To guarantee the better extraction conditions, some experimental variables were investigated. The recommended proportion for the microemulsion formation was 65% (v v(-1)) n-propyl alcohol, 20% (v v(-1)) gasoline, and 15% (v v(-1)) nitric acid solution. For the solid phase extraction, 100 mg of nanoferrite and a contact time of 10 min were recommended. Enrichment factors between 10 and 470 times were found for the analytes. The limits of detection obtained by the proposed method were 24, 2.8, 16 and 9.7 mu g L-1 for Cd, Cr, Cu and Pb, respectively. The precisions for determination of each element were expressed as relative standard deviations (RSD) using standard solutions containing 0.2 and 0.4 mg L-1 of each analyte and were between 2.0 and 8.1%. The developed method was applied in the determination of Cd, Cr, Cu and Pb in gasoline samples.