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/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 SO4 2- ions. The main interference was attributed to the interaction of some of these substances with copper oxides.

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.

Um seletivo método eletroquímico foi desenvolvido para determinação individual ou simultânea de paracetamol e cafeína em tampão fosfato pH 6,0, utilizando um eletrodo compósito impresso descartável à base de grafite e poliuretana (EIGPU), em Voltametria de Pulso Diferencial (DPV). Os picos de oxidação do paracetamol e cafeína aparecem em 0,3 V e 1,3 V (vs. pseudo-Ag/AgCl), respectivamente, mostrando a possibilidade de determinação simultânea de ambos analitos utilizando o EIGPU, além da determinação individual dos mesmos. A curva analítica da determinação simultânea mostrou uma resposta linear para as duas substâncias. O paracetamol apresentou uma região linear entre 1,00 - 40,0 µmol L-1 com limite de detecção de 0,84 µmol L-1 e a região linear da cafeína foi entre 4,00 - 200 µmol L-1, com limite de detecção de 1,6 µmol L-1. O método proposto foi aplicado na determinação simultânea de paracetamol e cafeína em três formulações farmacêuticas, com resultados que concordaram com HPLC ao nível de confiança de 95% (Teste t-Student).

A selective electrochemical method was developed for the individual or simultaneous determination of acetaminophen and caffeine in phosphate buffer pH 6.0 on graphite and polyurethane screen-printed composite electrode (EIGPU) using Differential Pulse Voltammetry (DPV). The oxidation peaks of acetaminophen and the caffeine appeared at 0.3 V and 1.3 V(vs. pseudo-Ag/AgCl), respectively, showing the possibility of simultaneous determination of both analytes, at the EIGPU, besides the individual determination. Analytical curves for the simultaneous determination showed a linear response for both compounds. The acetaminophen presented a linear region in the concentration range 1.00 - 40.0 µmol L-1 with detection limit of 0.84 µmol L-1, and the caffeine presented a linear region, in the concentration range 4.00 - 200 µmol L-1 with detection limit of 1.6 µmol L-1. The proposed method was applied in the simultaneous determination of acetaminophen and caffeine in three pharmaceutical formulations, with results similar to those obtained using a HPLC method, at 95% confidence level (Student t-Test).