Ultrasound-assisted cloud point extraction of manganese, zinc and tin from digested food samples for their determination by FAAS

Abstract

The current study is focused on the determination of the trace levels of manganese, zinc and tin in wet acid digested foods by flame atomic absorption spectrometry (FAAS) after preconcentration with ultrasound assisted-cloud point extraction (UA-CPE). The preconcentration procedure is making use of 2-(3,4-dihydroxyphenyl)-3,5,7-trihydroxy-4H-chromen-4-one (Quercetin) as the chelating agent, the cationic surfactant cetyltrimethylammonium bromide (CTAB) as the counter ion, the non-ionic surfactant polyoxyethylenesorbitan monolaurate (Tween 20) as the extracting agent, and acidic methanol as the diluting agent. The significant analytical parameters were optimized, and the selected values were a pH of 4.0, a chelating agent concentration of 8.5 μmol L⁻¹, cationic and nonionic surfactant concentrations of 30 μmol L⁻¹ and 0.5% w/v, a sample volume of 10 mL, an equilibrium temperature of 60 °C, an incubation time of 15 min and a diluting agent amount of 1.25 mL. Under optimum conditions, the detection limits for manganese, zinc and tin were 0.34, 0.15 and 0.7 μg L⁻¹ with sensitivity enhancement factors of 116, 175 and 153, respectively. The precision was evaluated as relative standard deviations (RSDs%) for solution containing 15 μg L⁻¹ of Mn(II), 40 μg L⁻¹ of Zn(II), and 20 μg L⁻¹ of Sn(II), and was found to be 2.3, 2.0 and 2.5% (n: 5), respectively. The accuracy of the method was evaluated by analysis of standard reference materials (SRMs) and through recovery rates from spiked aqueous samples. The obtained results were statistically in good agreement with the certified values at the 95% confidence limit, in which the recoveries for target analytes varied in the range of 95.6–104.2%. The method was successfully applied to the analysis of manganese, zinc and tin contents of various food samples, which are generally of plant origin, including black and green tea after dry ashing and wet digestion steps.