Development of a new method for extraction and preconcentration of cadmium and zinc ions in edible oils based on heat-induced homogeneous liquid–liquid microextraction

Abstract

A new sample preparation method, cyclohexylamine-based heat-induced homogeneous liquid–liquid microextraction, has been developed for the extraction and preconcentration of Cd(II) and Zn(II) ions in edible oils followed by flame atomic absorption spectrometry determination. First, the analytes are extracted into an acidic solution (a balanced mixture of HNO₃ and HCl). Second, they are preconcentrated via the microextraction method. Accordingly, cyclohexylamine (as a complexing agent and an extraction solvent) is added at µL-level into the obtained solution containing the analytes to form a homogeneous solution followed by the addition of sodium chloride. After manual shaking, the obtained solution is placed in a water bath thermostated at 60 °C. A cloudy solution because of the decrease in cyclohexylamine solubility in water at high temperature is formed. After centrifuging fine droplets of cyclohexylamine containing Cd(II) and Zn(II)—cyclohexylamine complexes are collected on the top of the aqueous phase. The preconcentrated analytes in the upper phase by use of flame atomic absorption spectrometry are analyzed and determined. Several variables possibly affecting the extraction efficiency were investigated and optimized. Under the optimum conditions, the calibration curves were linear in the ranges of 10–300 and 2.5–200 µg kg^− 1 for Cd(II) and Zn(II), respectively. Repeatability of the proposed method, expressed as relative standard deviation, was obtained 2.4 and 1.7% for Cd (II) and Zn(II), respectively. Moreover, the detection limits of the selected analytes were obtained 3.8 and 0.6 µg kg^− 1 for Cd(II) and Zn(II), respectively.