Application of simple, fast and eco-friendly ultrasound-assisted-cloud point extraction for pre-concentration of zinc, nickel and cobalt from foods and vegetables prior to their flame atomic absorption spectrometric determinations

Abstract

In this study, a simple, fast and eco-friendly ultrasound-assisted-cloud point extraction method for extraction and pre-concentration of zinc, nickel and cobalt from vegetables and foods prior to their determination by flame atomic absorption spectrometry (FAAS) was proposed. Ultrasound energy was used to shorten extraction time and reduce steps needed or to improve selectivity. The method is based on complex formation of metal ions with carmine in presence of cationic surfactant at pH 5.0, and then extraction of their hydrophobic complexes into the micellar phase of Igepal CO-630 as extractant. After optimisation, calibration curves for Zn, Co and Ni were linear in the range of 2-120, 2-220 and 2-180 g kg(-1), respectively. Limits of detection, which is described as ratio of 3xstandard deviation of 12 replicate measurements of blank analysis to slope of calibration curves, were 0.5, 0.6 and 0.6 g kg(-1) for Zn, Ni and Co, respectively. Relative standard deviations (RSDs%, n: 5) for 25 g kg(-1) of each analyte were less than 3.1%. The recovery rate was higher than 94% with a lower RSD than 3.1% for five replicate measurements of 25 g kg(-1) of each analyte. The accuracy was verified using two different standard reference materials (SRM 1570a-Trace elements in spinach leaves and SRM 1548a-Typical diet), and the results were in good agreement with the certified values. The method was applied to the determinations of Zn, Ni and Co in vegetables and foods by FAAS.