The present paper describes the sequential combination of dispersive magnetic solid phase extraction (DMSPE) with cloud point extraction (CPE) as a new nonchromatographic approach for preconcentration/redox speciation of chromium with FAAS detection. The method is based on sequential preconcentration of Cr(VI) at pH 5.0 onto mesoporous amino-functionalized Fe3O4/SiO2 nanoparticles followed by cloud point extraction of Cr(III) as metallic complex with 4-(2-thiazolylazo)resorcinol (TAR). The variables that play an important role on the performance of both preconcentration methods were thoroughly optimized by means of factorial design. Under optimized condition, an aliquot of 45.0 mL of sample was preconcentrated onto 25 mg of magnetic nanoparticles during 1 min following the elution with 0.5 mL of 2.5 mol L -1 HCl. The supernatant containing Cr(III) was then subjected to CPE procedure, in which was accomplished by using thermostatic bath at 90 o C during 45 min, 5.8 x 10 -4 mol L -1 TAR and 0.3% (v/v) Triton X-114. The method provided preconcentration factors of 16 and 12 times yielding limits of detection (LOD) and quantification (LOQ) of 1.1 and 3.6 µg L -1 for Cr(VI) and 3.2 and 10.5 µg L -1 for Cr(III), respectively. A high tolerance toward potentially interfering ions (cations and anions) and humic acid was observed for the method. Precision (n=10) of the procedure determined as relative standard deviation (RSD) were, 5.8 and 3.7% for Cr(III) using solutions at 15.0 and 165.0 μg L -1 and 5.5 and 3.0% for Cr(VI) using solutions at 15.0 and 75.0 μg L -1 concentrations, respectively. The applicability of method was attested by analysis of water samples yielding good recovery values (91.4-103.5 %). The accuracy of method was also checked for biological samples using a certified reference material DORM-3 (Fish Protein Certified Reference Material for Trace Metals).
A B S T R A C TThe use of alternative materials for environmental decontamination has been intensively studied. In this study, the capacity of banana peels treated with sodium hydroxide (NaOH), hydrochloric acid (HCl), and phosphoric acid (H 3 PO 4 ) to adsorb Pb (II) was evaluated. The physical and chemical changes on the banana peels after chemical treatment were evaluated by infrared spectroscopy and scanning electron microscopy. Batch adsorption experiments were carried out as a function of pH, time, metal concentration, and temperature; desorption tests were also performed. Pb (II) concentrations were determined by flame atomic absorption spectrometry. An increase in the adsorption capacity of the modified and natural peels was observed in the pH range of 3-5, and pH 5 was adopted for further experiments. The adsorption system reached equilibrium in 300 min, and its kinetics followed the pseudo-second-order equation. From adsorption isotherms, it was observed considerable enhance on adsorption capacity of banana peels, especially with treated with NaOH. Besides, the negative Gibbs free energy variation values showed that the Pb (II) adsorption was spontaneous. Moreover, the improvement in the Pb (II) desorption for the modified peels was observed, indicating that the proposed material can be reutilized.
Os rejeitos contendo metais pesados, originados de atividades industriais e mineradoras, podem ocasionar danos ao meio ambiente e à saúde humana. Mesmo o cromo, considerado um metal essencial, quando encontrado em altas concentrações, pode ser prejudicial, razão pela qual, o objetivo deste trabalho foi investigar a eficiência de tratamentos químicos em casca, bagaço e casca com bagaço de laranja, com o intuito de tratar efluentes aquosos contaminados por cromo (III). A modificação referese a alteração da estrutura química dos resíduos de laranja com hidróxido de sódio e ácido cítrico. Foram realizados ensaios em sistemas de batelada contendo cromo, sendo que as concentrações foram determinadas através da utilização de um espectrofotômetro de absorção atômica com chama. Analisouse a adsorção em função do pH, tempo de contato, concentração do metal, capacidade de dessorção e fatores termodinâmicos. As modificações foram constatadas no infravermelho pelo surgimento de um pico em 1730 cm-1 , o qual se refere aos grupos carboxilatos. O tempo necessário para o sistema de adsorção atingir o equilíbrio foi de cerca de 500 minutos e a cinética segue um comportamento descrito pela equação de pseudo-segunda ordem. Avaliou-se a adsorção em relação aos modelos de Langmuir e Freundlich, sendo o modelo de Freundlich o que se aplicou melhor ao processo. O valor da capacidade máxima de adsorção foi de 75,64 mg.g-1 para a casca modificada com NaOH. Além de aumentar as propriedades adsorventes, o sistema tornou-se mais espontâneo energeticamente após o tratamento químico, verificado pelos baixos valores da energia de Gibbs. Palavras-chave: Adsorção. Cromo. Resíduos de laranja. Modificação química.
In the present study, a flow injection system using dual mini-columns, SiO(2)/Al(2)O(3)/TiO(2) and silica gel functionalized with [3-(2-aminoethylamino)propyl] trimethoxysilane (SiO(2)/AAPTMS) for the sequential preconcentration of Cr(III) and Cr(VI), respectively, from water samples with FAAS detection was proposed. A two-level full factorial design (2(4)) and desirability function were employed for the optimization of variables related to the system performance. The detection limits of 0.66 and 0.27 μg L(-1) for Cr(III) and Cr(IV), respectively, were obtained under the optimized preconcentration conditions (flow rate of 7.0 mL min(-1)), pH 5.0, buffer concentration (acetate buffer) of 0.01 mol L(-1), and eluent (2.5 mol L(-1) HCl) flow rate of 5.0 mL min(-1). The other parameters including preconcentration factor (PF), consumptive index (CI), and concentration efficiency (CE) were found to be 17.62/32.98, 1.13/0.6 mL, and 6.2/11.54 min(-1) for Cr(III)/Cr(VI), respectively. The developed method was applied to the Cr(III) and Cr(VI) determination in water samples [tap, lake and mineral water, artificial saliva and parenteral solutions (physiological serum, water for injection, and glucose physiological solution)]. The method accuracy was checked by the analysis of standard reference materials (trace elements in water).
In this paper, we describe the synthesis of an ion imprinted polymer (IIP) by homogeneous polymerization and its use in solid-phase to extract and preconcentrate zinc ions. Under optimal conditions (pH 5.0, preconcentration flow rate of 12.0 mL min -1 , and eluted with 1.0 mol L −1 HNO 3 ) this procedure allows the determination of zinc with an enrichment factor of 10.2, and with limits of detection and quantification of 1.5 and 5.0 μg L −1 , respectively. The accuracy of our results was confirmed by analysis of tap water and certified reference materials: NIST 1570a (Spinach leaves) and NIST 1515 (Apple leaves).
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