Desenvolvimento de um método de microextração em fase sólida dispersiva assistida por ar e ultrassom para adsorção de íons Cd2+ utilizando pó de café magnetizado como adsorvente.

Abstract

Metal ions are non-biodegradable compounds that can be absorbed and penetrate the organism of living beings, causing serious risks, which can often be lethal. Thus, microextraction techniques combined with flame atomic absorption spectrometry (FAAS) have been used successfully in the determination of metallic ions even in trace quantities, aiming to contribute to the development of green chemistry. Therefore, this work aims to develop a methodology for the determination of trace-level metal ions through the air-assisted dispersive microextraction technique, using magnetized coffee powder as an adsorbent material. The coffee powder used was obtained from disposable coffee capsules, contributing to an adequate disposal of this residue. The material was initially washed with deionized water under stirring for 30 minutes and then dried at room temperature. For the magnetization procedure, previously synthesized magnetic fluid was used. For the adsorption tests, a solution of Cd(II) 1,0 mgL-1 and the pH, which is a parameter that affects adsorption, was evaluated in values from 3 to 9. According to the evaluation of the zero charge point of the adsorbent material obtained after magnetization, at pH 4,5 the surface of the adsorbent material is neutral . Thus, for the ion analyzed, in the pH range from 6 to 9 there was no significant difference in the percentage of adsorption, and pH 7 was selected for further studies, presenting an adsorption of 83.2%. In the air-assisted dispersive microextraction procedure, the extraction conditions (adsorbent mass and adsorption time) were optimized through the construction of a Doehlert matrix. The response surface obtained was characterized as a saddle point. However, as no lack of adjustment was observed and after analysis of the contour graph, the best adsorption conditions were obtained with the use of 42.5 mg of adsorbent and stirring for 16 minutes. The adsorption was better suited to the pseudo-second order kinetic model, reaching an equilibrium after 15 minutes. In optimizing the variables eluent concentration and desorption time, a response surface characterized as a maximum point was obtained. In which, it was adjusted to the experimental data, being obtained as optimal conditions for desorption the concentration of the eluent HCl 0.5 mol L-1 and desorption time of 8 min. The detection and quantification limit, sensitivity, precision (DPR) and pre-concentration factor values found for method validation were respectively 4.36 μg L-1 , 14.6 μg L-1 , 0.0011, 0.02% and 5.5 with a linear range 0.01 - 1250 μg L-1 for Cd(II). The repeatability and intermediate precision (or reproducibility) studies were respectively 1.6% and 4.2% indicating a good precision of the method, since the results were less than 20%. The selectivity of the method, which was performed both in the adsorption step and in the desorption step of the method, allowed to identify that the little interference of most of the ions evaluated happens in the desorption step. In the analytical performance a sensitivity of 0.0011 was obtained, linear working range of 15.6 – 1250 μg L-1 , a detection limit of 4.36 μg L-1 , a quantification limit of 14.6 μg L-1 and a preconcentration factor of 5.5. Method accuracy was evaluated from recovery tests on aqueous samples, with a recovery in the range of 80-120%. In this context, it can be concluded that the air-assisted dispersive microextraction technique using an aquarium pump and magnetized coffee powder as adsorbent material has been showing promising results in the process of adsorption of the Cd2+ ion, contributing to the development of clean analytical methodologies.