Amostragem direta de sorvente magnético em espectrometria de absorção atômica com chama para determinação de cádmio e chumbo em chás e cafés

Abstract

The technique of Direct Magnetic Sorbent Sampling in Flame Atomic Absorption Spectrometry (DMSS-FAAS) was recently proposed by the research group. DMSS-FAAS has demonstrated a significant improvement in detectability for the determination of potentially toxic metals in food samples, compared to other conventional techniques. A magnetic sorbent is used for a dispersive solid-phase extraction of the analytes in liquid samples, aiming at pre-concentration. The sorbent is captured at the tip of a magnetic probe, which is inserted directly into the FAAS flame for the atomization of the analytes. In this work, the magnetic biosorbent "Magnetic orange peel powder – M-OPP" was synthesized from dried and crushed orange peel, incorporating magnetite nanoparticles. M-OPP was characterized by Thermogravimetric Analysis, Fourier Transform Infrared Spectroscopy, Zeta Potential, Dynamic Light Scattering, Transmission and Scanning Electron Microscopy, Gas Sorption Porosimetry, Kinetics and Isotherm. Particle sizes of 27.20 ± 1.63 μm were obtained. The Toth and Sips models better explained the adsorption behavior of Cd and Pb in M-OPP, with maximum adsorption capacities of 0.51 and 9.02 mg g-1 , respectively. Univariate optimization for the pH of the samples was performed, followed by a complete factorial design 2³ of the extraction parameters: adsorption time, sorbent mass and sample volume. Then, eight calibration curves were constructed in different local commercial samples of teas and coffees for Cd and Pb, covering the working ranges of 5 to 40 μg L⁻¹ and 10 to 100 μg L⁻¹, respectively, which showed high correlations (r > 0.99) and acceptable precision and accuracy. The limits of quantification (LOQ) and detection (LOD) of the samples for Cd and Pb ranged from 5.00 - 10.00 μg L⁻¹ and 1.90 - 6.49 μg L⁻¹, respectively. Five real samples with Pb were quantified, but they were found to be below the maximum tolerated limit of 50 μg L⁻¹ by ANVISA. The experimental results showed that the DMSS-FAAS technique is feasible to analyze toxic metals, such as Cd and Pb, in teas and coffees, allowing their quantification at low concentrations. The technique has proven to be efficient, simple, fast, cost-effective and environmentally friendly for analyzing metals in food.