A disposable screen‐printed device containing working, auxiliary, and reference electrodes is proposed for the simultaneous voltammetric determination of Zn(II), Pb(II), Cu(II), and Hg(II) in ethanol fuel. The working electrode was printed using an ink modified with 2‐benzothiazole‐2‐thiol organofunctionalized SBA‐15 silica, in order to increase sensitivity. The performance of this electrode was compared with that of bare and SBA‐15‐modified electrodes. After optimizing the experimental parameters, the device was applied in determination of the analytes in commercial ethanol fuel samples, using 0.10 mol L−1 KCl/ethanol ratios of 30 : 70 (v/v), with [H+]=10−5 mol L−1. After 5 min of preconcentration at − 1.3 V (vs. pseudo‐Ag/AgCl), four well‐resolved signals were obtained, enabling simultaneous determination of the four analytes using a differential pulse anodic stripping voltammetry (DPASV) procedure. The limits of detection were 0.30, 0.065, 0.030, and 0.046 µmol L−1 for Zn(II), Pb(II), Cu(II), and Hg(II), respectively. The results of these analyses were in agreement with those obtained using graphite furnace atomic absorption spectroscopy (GFAAS) for Pb(II), Cu(II), and Hg(II), and high‐resolution continuum source flame atomic absorption spectrometry (HR‐CS‐FAAS) for Zn2+, at a 95 % confidence level. Analytes originally present in the samples could be detected, and the interference of some cations and anions was evaluated.
A graphite-polyurethane composite electrode (GPUE) was modified by electrodeposition of copper nanoparticles (CuNP) followed by electrochemical treatment in NaOH (GPUE-CuNP), in order to prepare an amperometric sensor for the determination of cysteine (Cys). Cyclic votammograms of Cys solutions at GPUE-CuNP allowed the description of a sequence of electrochemical reactions involving Cys oxidation and Cu 0 /Cu + equilibrium, generating a stable Cys-Cu + complex. The presence of these nanoparticles was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) data. Hence, the developed device was then used as a Cys amperometric flow detector in a wall-jet system, after evaluation of flow injection parameters in an undescribed approach. In this system, a limit of detection (LOD) of 4.24 μmol L -1 was obtained with an analytical frequency of 36 determinations h -1 . Intra-day and inter-day reproducibility and repeatability of the modified surface was evaluated. Then the GPUE-CuNP performance was investigated in the determination of Cys content in food supplements. Interference tests were carried out with pyridoxine, ascorbic acid, tryptophan and SO 4 2ions. The main interference was attributed to the interaction of some of these substances with copper oxides.
Recebido em 06/07/2015; aceito em 08/10/2015; publicado na web em 18/02/2015 USING SPREADSHEET SOFTWARE AS A TEACHING TOOL IN QUALITATIVE ANALYTICAL CHEMISTRY. The use of spreadsheet softwares is not widespread in Chemical Education in Brazil as a computational education tool. By its turn the Qualitative Analytical Chemistry is considered a discipline with classical and non-flexible content. Thus in this work the spreadsheet software Excel ® was evaluated as a teaching tool in a Qualitative Analytical Chemistry course for calculations of concentrations of the species in equilibrium in solutions of acids. After presenting the theory involved in such calculations the students were invited to elaborate the representation of the distribution of these species in a graphical form, using the spreadsheet software. Then the teaching team evaluated the resulting graphics regarding form and contents. The graphics with conceptual and/or formal errors were returned for correction, revealing significant improvement in the second presentation in all cases. The software showed to be motivating for the content of the discipline, improving the learning interest, while it was possible to prove that even in classical disciplines it is possible to introduce new technologies to help the teaching process.Keywords: software as teaching tool; Qualitative Analytical Chemistry; spreadsheet software; Excel ® .
INTRODUÇÃOO conteúdo das disciplinas do ciclo básico de um curso de Química reúne informações fundamentais, das quais não se pode prescindir quando se deseja uma formação de qualidade, pois seus conceitos são os fundamentos das aplicações e tecnologias modernas. Um forte exemplo disso é o conteúdo de Química Analítica Qualitativa, cujos conceitos embasam diversos aspectos da química, inclusive técnicas modernas de análise instrumental.Na maioria dos casos, os currículos dessa disciplina envolvem a apresentação do equilíbrio químico e suas aplicações aos sistemas ácido-base, de precipitação, complexação e óxido-redução. 1 Certamente, pouco se pode fazer quanto às mudanças de conteúdo dessa disciplina, porém é bem vindo que se usem estratégias para torná-la mais atraente e próxima da realidade dos alunos. Dentre essas estratégias pode-se lançar mão de recursos mais modernos de abordagem dos tópicos envolvidos, como já fazem algumas edições mais recentes de livros texto.
2,3A sociedade contemporânea está repleta de novas tecnologias que oferecem acesso às informações e promovem evolução constante do conhecimento. Um dos principais fatores desses avanços rápidos são, sem dúvida, as Tecnologias da Informação e Comunicação (TICs), cada vez mais presentes no cotidiano das pessoas. Essas tecnologias estão presentes a tal ponto que alguns autores chegam a considerar que aqueles indivíduos que não se familiarizarem com elas correm o risco de tornarem "analfabetos tecnológicos", 4 podendo ficar à margem da sociedade, quando se pensa em formação profissional.Sendo o professor um mediador do conhecimento, na ótica de Vygotsky, 5 seria interessant...
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