Extraction induced by emulsion breaking

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The extraction of polar and/or metal traces from oily samples is an analytical challenging task due to the nature of the sample matrix. Casella et al. proposed, in 2010, the extraction induced by emulsion breaking technique which faced up this challenge with high success (1). This technique is based on the formation of a stable emulsion between the oily sample (diesel, oil etc.) and an aqueous phase that contains a surfactant. The surfactant promotes the emulsification of both phases favoring their contact and therefore, making easier the transference of the analytes from the non-polar to the polar phase. After the extraction, the emulsion should be broken, usually by centrifugation, in order to allow phase’s separation and the final analysis of the aqueous phase.

In a recent article, accepted for publication in Talanta, the same authors have proposed a similar approach for the determination of Cu, Fe and Mn in used lubricating oils (2). This determination is quite important since it provides information about the state of the engine and it also interesting for the characterization of this waste.

The proposed extraction follows the general guidelines of extraction induced by emulsion breaking, previously described. In this case, the lubricating oil is diluted, before the extraction step, with toluene to reduce the viscosity and to enhance the mass transference. The diluted oil is finally extracted with an aqueous phase containing Triton X-114 (as emulsifier) and nitric acid (as extracting compound). After the extraction, and the intrinsic centrifugation step, the aqueous phase is finally analyzed by flame absorption atomic spectrometry.

The proposed methodology provides limits of detection in the range of ng/g and excellent accuracy when it is compared to the classical analytical method based on the sample mineralization.

The readers are referred to the original manuscript where the optimization process (including several variables) and the analytical characterization are described in detail.


References:

(1) Extraction induced by emulsion breaking: a novel strategy for the trace metals determination in diesel oil samples by electrothermal atomic absorption spectrometry. Link to the article

(2) Application of the extraction induced by emulsion breaking for the determination of Cu, Fe and Mn in used lubricating oils by flame atomic absorption spectrometry. Link to the article

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