Extraction induced by microemulsion breaking as a novel tool for the simultaneous determination of Cd, Mn, Pb and Sb in gasoline samples by ICP-MS and discrete sample introduction

This study reports a simple and efficient method for the simultaneous determination of Cd, Mn, Pb, and Sb at trace levels in gasoline samples by discrete sample introduction in inductively coupled plasma mass spectrometry (ICP-MS), employing the extraction induced by microemulsion breaking as a sample preparation method. In this work, a microemulsion was formed by mixing 0.7 mL of the gasoline sample with 0.28 mL of ethanol and 0.02 mL of 7 mol L-1 HNO3 solution. Afterwards, 0.1 mL of ultrapure water was added to induce microemulsion breaking. This lead to the formation of two different phases: (i) a top organic phase and (ii) a bottom aqueous phase that contained acid, ethanol and the extracted analytes. After that, 20 mu L of the bottom phase (extract) was collected, and the analyte concentrations were determined by discrete sample introduction in ICP-MS. Calibration curves with 20 mu g L-1 of Rh as an internal standard were set up to each analyte in the range from 1 up to 10 mu g L-1, wherein the standard solutions were prepared in the matrix-matched extract (70:25:5, ethanol: deionized water: 7 mol L-1 HNO3 solution). The optimization of the EIMB conditions was carried out by analyzing the effects of the parameters that could affect the extraction efficiency, such as the relation between the nature of the alcohol and the proportion of the volumes of the microemulsion constituents (sample, HNO3 and alcohol), acid concentration, and the water volume used for the microemulsion breaking. The following limits of detection relative to the amount of sample were obtained: 0.03 (Cd), 0.49 (Mn), 0.07 (Pb) and 0.02 (Sb), all of them in mu g L-1. The accuracy of the method was evaluated by the analysis of spiked samples, because no certified gasoline reference material is available. The average recoveries achieved for every analyte ranged from 96% to 114%. The developed methodology was successfully applied to the determination of these metals in five commercial gasoline samples.