A reliable determination of zinc levels in beverages with and without alcohol by flame atomic absorption spectrometry after cloud point extraction

Abstract

Cloud point extraction (CPE) has been used for the preconcentration and quantification of zinc after the formation of a stable complex with N-phenylbenzohydroxamic acid (PBHA) at pH 9.0 and analysis by flame atomic absorption spectrometry (FAAS) using polyethylene glycol tert-octylphenyl ether (Triton X-114) as the extracting surfactant. The chemical variables affecting the phase separation and the viscosity affecting the detection process were optimized. A preconcentration of only 50 mL of sample in the presence of 0.02% (w/v) Triton X-114 and 2.0 × 10⁻⁴ mol L⁻¹ PBHA permitted the detection and quantification of 0.42 and 1.41 μg L⁻¹ zinc, respectively. The improvement and preconcentration factors were 74.2 and 50 for zinc, respectively. The accuracy was controlled by analysis of the certified reference materials, SRM 1515 and SRM 1573a. The obtained results were in good agreement with the certified values. The proposed method was successfully applied to the determination of trace levels of zinc in beverage samples with satisfactory results. The results of zinc determination in the digested samples with HNO₃/H₂O₂ (3 : 1, v/v) are in agreement with that in the digested samples with HNO₃/HClO₄ (5 : 1, v/v). Zinc levels are in the range of 44.40–110.15 μg L⁻¹ with standard deviation values ranging from 1.35 to 2.65 μg L⁻¹ for the canned beverages without alcohol and 35.65–135.80 μg L⁻¹ with standard deviation values ranging from 1.10 to 3.50 μg L⁻¹ for the beverages with alcohol.