Ultrasonic-assisted dispersive liquid–liquid microextraction (US DLLME) of zinc in Brazilian sugarcane spirit samples

Abstract

A method based on the dispersive liquid–liquid microextraction for the pre-concentration of zinc in samples of Brazilian cachaca and determination by flame atomic absorption spectrometry (FAAS) was developed. The procedure is based on the injection of a mixture composed of carbon tetrachloride (extractor) and 5-(4-dimethylaminobenzylidene) rhodamine (complexing) in cachaca samples. The composition of the components of microextraction was univariable optimized. Posteriorly, a two-level fractional factorial design (26−2) was performed to evaluate the significance of the variables, pH, buffer concentration, centrifugation time, sonication time, NaCl concentration and temperature. Analysis of the Pareto graph showed that the pH, NaCl concentration and sonication time are statistically significant. These variables were optimized using the Doehlert matrix, which was obtained as better experimental conditions: pH, 9.0; %NaCl, 4% (m v−1); sonication time, 5.5 min. The precision expressed as relative standard deviation (RSD) was 3.43% for 20 μg L−1, the limit of detection was 0.11 μg L−1, and the limit of quantification was 0.33 μg L−1. The pre-concentration factor of the method was 28. The method was applied for the analysis of Brazilian sugarcane spirit, and the concentration of zinc ranged from 1.35 to 12.5 μg L−1.