Extraction induced by emulsion breaking: a novel strategy for the trace metals determination in diesel oil samples by electrothermal atomic absorption spectrometry

Abstract

This present work reports a novel strategy for the extraction of metals (Cu, Fe, Ni and Pb) from diesel oil and their determination by Electrothermal Atomic Absorption Spectrometry (ETAAS). The method is based on the formation of water-in-oil emulsions by vigorous mixing of the samples with a Triton X-114 solution containing HNO₃ and posterior breaking of the emulsion by heating. After the emulsion breaking, three well separated phases were obtained: (i) the upper phase, which is an organic phase containing only the diesel oil, (ii) an acidic aqueous phase containing the extracted metals and (iii) the lower phase, which is a surfactant-rich phase. The metals were concentrated in the aqueous phase, as a result of their acidic extraction from diesel oil. Several parameters that could influence the extraction efficiency and the time required to break the emulsions were evaluated such as the concentration and nature of the surfactant (Triton X-100 and Triton X-114), the HNO₃ concentration and the temperature. At best conditions, the emulsions were prepared by mixing 10 mL of diesel oil with 2 mL of a solution containing 7% w/v Triton X-114 and 10% v/v HNO₃. Afterwards, the emulsions were broken by heating at 80 °C for 15 min and then, the aqueous phase was collected and the metals were determined by ETAAS using external calibration with aqueous standard solutions. The limits of detection for Cu, Fe, Ni and Pb were equal to 114, 183, 145 and 294 ng L⁻¹ and the limits of quantification were 380, 609, 484 and 980 ng L⁻¹, respectively. These limits were estimated for the original sample taking into account the preconcentration factor obtained due to the Extraction Induced by Emulsion Breaking (EIEB) application. The novel strategy was applied in the analysis of five samples of diesel oil and the obtained results fitted well with those obtained by the reference method. Also, a recovery test was performed by spiking the samples with known amounts of the metals in the form of organometallic standards and thus applying the proposed procedure. The recoveries were in the range of 85.2–109%.