Continuous homogeneous liquid –liquid microextraction for the extraction of Cd(II), Cu(II), and Zn(II) ions from oil samples based on in-situ preparation of a deep eutectic solvent

A microextraction technique was developed for analyzing Cd(II), Cu(II), and Zn(II) ions in oil samples utilizing continuous homogeneous liquid-liquid microextraction followed by atomic absorption spectrophotometry. This method involved in-situ formation of a deep eutectic solvent from glycolic acid and choline chloride. The solvent was generated by passing the mixture of constitutes through a syringe barrel containing thermogenic salts. The heat released during the salts dissolution increased the solution’s ionic strength, aiding the solvent formation. Factors affecting extraction efficiency, including type and amount of salts, components of the deep eutectic solvent, and flow rate were examined. Calibration curves for Cd(II), Zn(II), and Cu(II) ions showed linear ranges from 0.8 to 100 μg kg⁻¹. The detection limits were 0.4, 0.8, and 0.3 μg kg⁻¹ for Cu(II), Cd(II), and Zn(II), respectively. The method’s repeatability, indicated by relative standard deviation ranged from 4.2 % to 5.3 % (n = 6, C = 25 μg kg⁻¹). The accuracy of the optimized method was investigated with the analysis of the selected ions in a certified reference material; EnviroMAT HU-1. Overall, this method was sensitive, rapid, environmentally friendly, and effective method for extracting and determining Cd(II), Cu(II), and Zn(II) in oil samples.