A molecularly imprinted polymer (MIP) was prepared using the anti-inflammatory diclofenac (DCF) as a template. A non-imprinted polymer (NIP) was also prepared as a control. These MIP and NIP were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer-Emmett-Teller (BET), revealing a higher porosity in the first. Then both were used in the modification of graphite-polyurethane composites electrodes (GPUE). Differential pulse anodic stripping voltammetry was used for DCF determination at GPUE MIP DCF containing 2.5% (m/m) of the modifier in perchloric acid, pH = 2.0, after previously optimized conditions such as 300 s of accumulation time, +0.2 V accumulation potential (vs. SCE (saturated calomel electrode)), 50 mV pulse amplitude and 10 mV s-1 scan rate. A linear dynamic range from 0.010 to 0.20 μmol L-1 and a limit of detection (LOD) of 0.99 nmol L-1 were found, using GPUE 2.5 MIP DCF. DCF was determined in commercial pharmaceutical formulations and in synthetic urine samples, with recoveries between 101 and 102% (n = 3) and 101% (n = 3), respectively. The results agreed with the reference high-performance liquid chromatography (HPLC) within 95% confidence level, according to Student’s t-test. Interference from meclofenamic and mefenamic acids, which are structurally similar to DCF, was also evaluated. Interferences could not be totally avoided, but MIPs presented a considerable ability in discriminating the voltammetric response for DFC, despite the close structural similarity with the interferents.

Teaching laboratory of qualitative analytical chemistry is still a controversial issue in chemistry courses. However, important researchers and educators in chemistry recognized and highlighted the importance that the contents of this discipline represent in the formation of chemists, once it can provide handling and understanding of microscopic phenomena based on the observation of their macroscopic effects, once such reactions and phenomena are the basis of important instrumental methods of analysis. Thus, a proposal based on a bottom-up approach has been developed, starting with the observation of different reactions of cations in laboratory, followed by a search for the reaction responsible for each resulting phenomenon observed during the experimental step. Then these reactions are related with the separation procedures of each group of cations. Eventually the separation of these groups can also be performed depending on the time available. The proposal has been applied in teaching laboratory of qualitative analytical chemistry at Instituto de Química de São Carlos/USP since 2015, where the discipline is offered duirng 4 hours/week, and a positive feedback regarding the evolution of the methodology and its acceptance by students. Good results were also obtained concerning the appropriation of the contents by the students, using the proposal.

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.

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).

A determinação de triptofano usando voltametria de varredura rápida com um ultramicroeletrodo de fibra de carbono (CF-UME) é descrita. O eletrodo CF-UME foi submetido a um pré-tratamento eletroquímico. Parâmetros tais como número de aquisição de ciclos, velocidade de varredura, intervalo de potencial e pré-tratamento eletroquímico da superfície foram otimizados. Sob condições ideais, três curvas analíticas foram obtidas para o triptofano (entre 30 e 300 µmol L-1) usando três diferentes CF-UME pré-tratados através de um procedimento de tratamento eletroquímico otimizado. Observou-se uma dependência na sensibilidade e concentração do triptofano com o raio do eletrodo, com limites de detecção entre 16,7 e 22,7 µmol L-1. O método foi aplicado na determinação de triptofano em amostras comerciais com erros entre -0,99 e +13,2% em relação a um método comparativo

Tryptophan determination using a fast-scan voltammetric method at carbon fiber ultramicroelectrodes (CF-UME) is described. CF-UME electrode was submitted to electrochemical pretreatment. Parameters such as number of acquisition cycles, scan rate, potential interval and electrochemical surface pretreatment were optimized. Under optimized conditions, three analytical curves were obtained for tryptophan (between 30 and 300 µmol L-1) using three different CF-UMEs pretreated by means of an optimized electrochemical treatment procedure. It was observed a dependence on the sensitivity and tryptophan concentration linear range with the radius of the electrode, with limits of detection between 16.7 and 22.7 µmol L-1. The method was applied in the determination of tryptophan in commercial samples, with errors between -0.99 and +13.2% in relation to a comparative method.

O eletrodo compósito grafite-poliuretana foi avaliado na determinação de tetraciclina (TC) em amostras de água natural. Utilizando voltametria de pulso diferencial (DPV), uma resposta linear foi observada no intervalo de 4,00-40,0 µmol L-1 com limite de detecção de 2,80 µmol L-1, sem necessidade de renovação da superfície entre medidas sucessivas. Durante determinação de tetraciclina em amostras de água, foram obtidas recuperações entre 92,6 e 100%. Os resultados para determinação de TC em amostras de água após a etapa de pré-concentração concordam com valor adicionado em um nível de confiança de 95% de acordo com o teste t-student.

A bare graphite-polyurethane composite was evaluated in the tetracycline (TC) determination in natural water samples. Using differential pulse voltammetry (DPV), a linear response was observed in the range of 4.00-40.0 µmol L-1 with limit of detection of 2.80 µmol L-1, without the need of surface renewing between successive runs. During the tetracycline determination in water samples, recoveries between 92.6 and 100% were found. The results for TC determination in water samples after a pre-concentration stage agreed with spiked value at a 95% confidence level according to student t-test.

Um eletrodo compósito de grafite-poliuretana sem modificação foi avaliado como um detector amperométrico para análise em fluxo, na determinação de paracetamol (APAP) em formulações farmacêuticas. Uma curva analítica foi obtida com região linear entre 5,00 x 10-5 e 5,00 x 10-3 mol L-1, com um limite de detecção de 18,9 µmol L-1 e 180 determinações por hora, depois de parâmetros otimizados como potencial de detecção, volume de amostragem, e vazão da solução carregadora. Interferência de ácido ascórbico foi observada, entretanto foi possível contorná-la, como visto pelos resultados que concordaram com HPLC com nível de confiança de 95%. Estes resultados mostraram que o compósito grafite-poliuretana pode ser usado como um detector amperométrico para análise em fluxo na determinação de APAP.

A bare graphite-polyurethane composite was evaluated as an amperometric flow injection detector in the determination of paracetamol (APAP) in pharmaceutical formulations. A linear analytical curve was observed in the 5.00 x 10-5 to 5.00 x 10-3 mol L-1 range with a minimum detectable net concentration of 18.9 µmol L-1 and 180 determinations h-1, after optimization of parameters such as the detection potential, sample loop volume, and carrier solution flow rate. Interference of ascorbic acid was observed, however, it was possible overcome the interference, reaching results that agreed with HPLC within 95% confidence level. These results showed that the graphite-polyurethane composite can be used as an amperometric detector for flow analysis in the determination of APAP.

A composite electrode prepared by mixing a commercial epoxy resin Araldite® and graphite powder is proposed to be used in didactic experiments. The electrode is prepared by the students and applied in simple experiments to demonstrate the effect of the composite composition on the conductivity and the voltammetric response of the resulting electrode, as well as the response in relation to the scan rate dependence on mass transport. The possibility of using the composite electrode in quantitative analysis is also demonstrated.

Graphite powder was mixed to polyurethane, silicon rubber and Araldite® (epoxy) in order to prepare composite materials to be used in the preparation of electrodes. Results showed that voltammetric response could be obtained when at least 50% of graphite (w.w-1) is present in the material. SEM and thermogravimetry were also used in the characterization of the composites.