Ultrasound-vortex assisted extraction combined with homogeneous liquid-liquid extraction for extraction and preconcentration of Cd and Zn from edible oils

Trace elements can be naturally present in edible oils, because of contamination from the soil and fertilizers where the plants were grown [1].The accurate determination of trace metals in this kind of samples is still an analytical challenge, owing to their low concentration level and the difficulties that arise due to the characteristics of the matrix [2]. Homogeneous liquid-liquid extraction (HLLE), utilizes a phase separation phenomenon in a homogeneoussolution. One version of HLLE is salting-out homogenous liquid-liquid extractionwhich has been used for extraction and preconcentration of the selected analytes from aqueous samples [3].A new sample preparation method has been developed for the extraction and preconcentration of Cd and Zn from edible oils based on HLLE. Initially, a 1:1 mixture of 1% HNO3 and 0.2% HCl(8 mL) were added to an oil sample. The mixture was vortexed and ultrasonic vibration was then used to effectively extraction of the analytes into the acidic phase. The phases were separated by centrifugation, and the extracted analytes in the acidic aqueous phase were pre-concentrated by the proposed HLLE. Therefore, cyclohexylamine(as extraction solvent) was added at µL level to the obtained solution containing Cd(II) and Zn(II), and a homogeneous solution was formed. Then NaCl was added to the solution, and a cloudy solution was formed. The enriched analytes in the upper phase (cyclohexylamine containing the formed complexes) were determined by flame atomic absorption spectrometry. Several variables possibly affecting the extraction efficiency were investigated and optimized. Under the optimum conditions the calibration curves were linear in the range of 30-300 µg L-1. Repeatability of the proposed method, expressed as relative standard deviation, ranged from 3.5-4.5%.Finally, the proposed method was successfully applied for the simultaneous analysis of the selected analytes in different oil samples.