Ultrasound-Assisted Dispersive Liquid-Liquid Microextraction Based on Melting of the Donor Phase: a New Approach for the Determination of Trace Elements in Solid Samples

Abstract

A novel ultrasound-assisted dispersive liquid-liquid microextraction (UA-DLLME) based on melting of the donor phase for the determination of Cd, Cu, and Fe in margarine samples using high-resolution continuum source electrothermal atomic absorption spectrometry (HR-CS ET AAS) is proposed. Considering that margarine is in the solid phase at room temperature, requiring heat for melting, the microextraction process was assisted by an ultrasonic bath to ensure the melting point of the samples and to increase the extraction efficiency of the analytes by UA-DLLME. After the extraction procedure, the aqueous phase was collected and directly introduced into a graphite furnace. The procedure was applied for extraction and multi-element determination, exploring the strategy of simultaneous and sequential determination of analytes by HR-CS ET AAS. A low volume of nitric acid solution in the presence of ethanol and hydrogen peroxide allowed the metals to be separated from the sample in an aqueous phase with subsequent determination by HR-CS ETAAS. In the extraction procedure, 5.0 g of each margarine sample was sonicated under heating in the presence of 100 μL of a solution containing HNO3 0.1 mol L−1, ethanol (95.1%, v v−1), and H2O2 3% (v v−1) in a volume proportion of 2:1:1. The influences of the time of extraction, temperature of extraction, and amplitude of sonication were examined, and the proposed conditions were as follows: extraction time, 10 min; temperature, 60 °C; and amplitude, 100%. Using 5 g of margarine sample, limits of detection of 0.03, 0.52, and 224 ng g−1 were obtained for Cd, Cu, and Fe, respectively. Recovery tests were performed, and the results ranged from 87 to 108% for Cd, 91 to 115% for Cu, and 85 to 112% for Fe. The results obtained by the proposed extraction procedure agreed with those obtained after wet digestion of the sample and determination by inductively coupled plasma optical emission spectrometry (ICP OES).