Reverse dispersive liquid-liquid microextraction for the isolation of Cd and Pb from edible oils

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Dispersive liquid-liquid microextraction (DLLME) is a consolidated sample treatment technique which is characterized by its high efficacy leading to high enrichment factors. In the normal mode, the technique consists of the dispersion of a mixture of disperser and extraction solvents into the aqueous sample. The dispersion forms a cloudy state consisting of a innumerable extractant droplets which favors the transference of the analyte from the bulk sample. Hashemi et al. (1) adapted this technique to the extraction of non-aqueous phases giving rise to the so-called reverse phase DLLME (RP-DLLME).

Reverse DLLME has been recently applied by researchers of the University of Murcia (Spain) for the extraction of cadmium and lead from edible oils (2). This is a problem of concern due to the inherent toxicity of both elements and their capability to influence some oxidative reactions that may lead to toxic compounds. To perform the RP-DLLME the sample is extracted with a mixture containing isopropyl alcohol (disperser solvent) and a nitric acid solution (extraction phase), the latter being isolated by means of a centrifugation step and finally analyzed by electrothermal atomization atomic absorption spectrometry (ETAAS). The negative effect of the sample viscosity on the dispersion of the solvents mixture is easily overcome by heating the sample at 80 ºC before the RP-DLLME.


The proposed methodology provides limits of detection for both elements in the low ng/Kg which are better than those obtained with other counterparts.

We encourage the reading of the article where the complete optimization (the selection of the dispersion solvent is quite interesting) and validation is described. Moreover the analysis of real samples, comprising not only common edible oils (olive, sunflower or soy) but also nutritional supplements, is also remarkable.

References:
(1) Reversed-phase dispersive liquid–liquid microextraction with central composite design optimization for preconcentration and HPLC determination of oleuropein. Link to the article

(2) Determination of cadmium and lead in edible oils by electrothermal atomic absorption spectrometry after reverse dispersive liquid–liquid microextraction. Link to the article

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