A molecularly imprinted electrochemical sensor for determination of isoamyl alcohol was successfully constructed by modifying the glassy carbon electrode (GCE) with gold nanoparticles (AuNPs) and reduced graphene oxide (RGO). The modification of the GCE increased the electron transfer rate and the electrode surface area, which, consequently, made more room available for the formation of the molecularly imprinted polymer (MIP). The development of the MIP on the modified surface was carried out via electropolymerization of the pyrrole in acetate buffer solution in the presence of the target molecule. The MIP-AuNPs-RGO/GCE showed low limit of detection (8.4 × 10-8 mol L-1), satisfactory quantification range, amperometric sensitivity of 1.1 A L mol-1, excellent reproducibility and stability. Even when in the presence of analogous molecules, the sensor exhibited excellent selectivity. These results suggest that the proposed sensor is suitable for the detection of isoamyl alcohol in fusel oil samples.

This work aims to present an alternative detector for the determination of arabinose, galactose, glucose and xylose in hydrolyzed sugarcane bagasse. The detector was developed using an electrode modified with multi-walled carbon nanotubes containing cobalt oxide nanoparticles (GCE/MWCNT/CoOOH) applied in high-performance liquid chromatography (HPLC) with reverse pulsed amperometric detection (RPAD). The limits of detection obtained were 3.4 × 10-6, 4.4 × 10-6, 3.6 × 10-6 and 5.0 × 10-6 mol L-1 for arabinose, galactose, glucose and xylose, respectively. The standard addition method was used to determine the concentration of sugars in the hydrolyzed sugarcane. The determined concentrations for arabinose, galactose, glucose, and xylose were 1.0 × 10-3, 7.2 × 10-5, 3.0 × 10-3 and 2.4 × 10-3 mol L-1, respectively. The results demonstrate that this new method can be used for the detection of sugars without the interference of other electroactive species.

The electrochemical behavior of the interaction of amodiaquine with DNA on a carbon paste electrode was studied using voltametric techniques. In an acid medium, an electroactive adduct is formed when amodiaquine interacts with DNA. The anodic peak is dependent on pH, scan rate and the concentration of the pharmaceutical. Adduct formation is irreversible in nature, and preferentially occurs by interaction of the amodiaquine with the guanine group. Theoretical calculations for optimization of geometry, and DFT analyses and on the electrostatic potential map (EPM), were used in the investigation of adduct formation between amodiaquine and DNA.

Neste trabalho, a redução eletroquímica do amebicida Teclozan (TEC) foi estudada sobre um eletrodo de carbono vítreo em meio de acetonitrila. Eletrólises com potencial controlado foram realizadas visando, tanto a determinação do número de elétrons envolvidos na redução do fármaco, quanto a identificação dos produtos eletrogerados, os quais foram isolados por extração líquido-líquido e caracterizados por ¹H RMN. Foi verificado que o TEC apresenta dois picos voltamétricos, cada um associado à quebra redutiva de duas ligações C-Cl. Em presença de um doador de prótons, foi observado que o primeiro pico voltamétrico em -1,8 V corresponde principalmente à redução dos grupamentos -CHCl2 a -CH2Cl; enquanto o segundo pico em -2,2 V é responsável pela redução dos grupos -CH2Cl a CH3, fornecendo como único produto o derivado totalmente desalogenado do TEC, com rendimentos entre 82 e 97%. Este trabalho descreve também o desenvolvimento de um método eletroanalítico baseado na detecção amperométrica do TEC em condições hidrodinâmicas, o qual forneceu um limite de detecção de 8,9 × 10-6 mol L-1.

The electrochemical reduction of amoebicide Teclozan (TEC) was studied on a glassy carbon electrode in acetonitrile. Controlled-potential electrolyses were performed for coulometric and preparative purposes. The electrogenerated products were isolated by liquid-liquid extraction and characterized by ¹H NMR. It was observed that TEC presents two voltammetric peaks, each one associated with the cleavage of two C-Cl bonds. In presence of a proton donor it was observed that the first peak at -1.8 V promotes mainly the reduction of the groups CHCl2 to CH2Cl and the second one at -2.2 V promotes the reduction of the groups CH2Cl to CH3 giving as the sole product the completely dechlorinated TEC derivative with yields between 82 and 97%. In addition, a comparative study between the analytical performance of voltammetric techniques and amperometric detection of TEC in hydrodynamic conditions was performed. The amperometric detection was more sensitive than all evaluated voltammetric techniques, providing a detection limit of 8.9 × 10-6 mol L-1.

A square wave voltammetric method is described for the determination of acetaldehyde using the derivatization reaction with hydrazine sulphate, based on the reduction of hydrazone generated as a product that exhibits a single well-defined peak at -1.19V in acetate buffer at pH 5. Calibration graphs were obtained from 1.0 x 10-6 mol L-1 to 10 x 10-6 mol L-1 of acetaldehyde, using a reaction time of 8 min and a hidrazine concentration of 0.02 mol L-1. The detection limit was 2.38 x 10-7 mol L-1. The method was applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pre-treatment.

A redução eletroquímica do Furoato de Diloxanida (FD) em acetonitrila sobre um eletrodo de carbono vítreo foi estudada neste trabalho. Foi observado que o FD é reduzido após uma transferência reversível de um elétron seguida por uma reação química irreversível, diagnosticada, como uma ruptura de uma ligação C-Cl. A redução do FD foi estudada por voltametria de varredura linear (LSV), pulso diferencial (DPV) e onda quadrada (SWV). Curvas analíticas foram obtidas usando todas as técnicas voltamétricas estudadas. Para a técnica de LSV obteve-se um intervalo linear (LR) de 5,0 x 10-4 a 1,0 x 10-2 mol L-1, com limite de detecção (DL) de 1,5 x 10-4 mol L-1 e sensibilidade (S) de 2,1 x 10(4) µA mol-1 L . Os parâmetros analíticos obtidos com a técnica de DPV foram: LR = 5,0 x 10-4 a 2,2 x 10-3 mol L-1, DL = 7,8 x 10-5 mol L-1, S = 3,7 x 10(4) µA mol-1 L. Para a técnica de SWV foram obtidos os seguintes parâmetros analíticos LR = 7,5 x 10-6 a 1,2 x 10-3 mol L-1, DL = 5,5 x 10-6 mol L-1 e S = 2,8 x 10(5) µA mol-1 L. Assim, a técnica de SWV foi a mais sensível, podendo ser empregada para a quantificação de FD em baixos níveis de concentração. Métodos estatísticos foram utilizados para avaliar o procedimento analítico, recuperações próximas a 100% e desvios padrão relativos inferiores a 5,0% (N=5) foram obtidos. Através do teste-t verificou-se que não há evidências de erros sistemáticos em nenhuma das técnicas estudadas.

The electrochemical reduction of diloxanide furoate (DF) in acetonitrile on glassy carbon electrode was studied in this work. It was observed that DF is reduced after a reversible one-electron transfer followed by an irreversible chemical reaction, diagnosed as C-Cl bond cleavage. Its reduction was followed by linear (LSV), differential pulse (DPV) and square wave voltammetry (SWV). Analytical curves were obtained for DF determination using all the investigated voltammetric techniques. For LSV was obtained a linear range (LR) from 5.0 x 10-4 to 1.0 x 10-2 mol L-1, with detection limit (DL) of 1.5 x 10-4 mol L-1 and sensitivity (S) of 2.1 x 10(4) µA mol-1 L. The analytical parameters obtained by DPV were: LR = 5.0 x 10-4 to 2.2 x 10-3 mol L-1, DL = 7.8 x 10-5 mol L-1, S = 3.7 x 10(4) µA mol-1 L. For SWV were obtained a LR = 7.5 x 10-6 to 1.2 x 10-3 mol L-1, DL = 5.5 x 10-6 mol L-1 and S = 2.8 x 10(5) µA mol-1 L. Thus, the SWV was the most sensible technique, which can be used for DF determination at low concentration levels. Statistics methods were used to evaluate the analytical procedure, where recovery around to 100% was obtained for all voltammetric techniques. Relative standard deviations were lower than 5.0% (N=5). The obtained t values evaluating all the three voltammetric methods were less than the tabulated ones, indicating that there are no evidences of systematic error.

A remoção do corante reativo Reactive Blue 4 (RB4) por redução eletroquímica em solução aquosa foi investigada sobre eletrodo de carbono vítreo reticulado. O grupo antraquinona presente no corante RB4 é reduzido em pH < 8,0 em uma única etapa a hidroquinona, segundo um processo reversível de dois elétrons e reação de pré-protonação, via geração de um radical semiquinona detectado espectrotométricamente. Em pH > 8,0, ambas as formas não e pré-protonada da antraquinona são reduzidas em duas etapas reversíveis de dois elétrons. Após 3 horas de eletrólise em meio ácido e neutro o corante perde 60% de sua coloração, enquanto que em meio alcalino perde apenas 37%. Simultaneamente, 64% de remoção de carbono orgânico total foi obtida após eletrólise em meio ácido de pH 2,0.

The electrochemistry reduction for the removal of Reactive Blue 4 (RB4) dye from aqueous solution using reticulated glassy carbon electrode is investigated. At pH < 8.0 the anthraquinone group of the RB4 dye are reduced in one cathodic step to hidroquinone after a reversible two-electron process involving a precedent two protons reaction. A stable semiquinone is detected by spectrophotometric technique. At pH > 8.0 the reduction process involves two reversible 2-electron steps, whose species are generated by a protonation equilibrium of anthraquinone group. The results shows that 60% of color removal was obtained after 3 hours of RB4 dye electrolysis at acidic and neutral conditions and only 37% at alkaline conditions. Simultaneously 64% of total organic carbon was removed after electrolysis at pH 2.0.

Procion Green HE-4BD is a reactive dye currently used in affinity purification, and commonly present as a contaminant in the final biological preparation. An assay method is described to determine trace amounts of the dye in the presence of human serum albumin(HSA) and leakage from agarose as affinity sorbent by cathodic stripping voltammetry. The proposed method is based on the reductive peak at -0.55V in B-R buffer pH 3 (E=0V and t= 240s), obtained when samples of HSA 2% (m/v) containing dye concentrations in sodium hydroxide pH 12 are submitted to a heating time of 330 min at 80 ºC. Linear calibration curves can be obtained for RG19 dye concentrations from 5x10-9 mol L-1 to 8 x10-8 mol L-1. The detection limit (3sigma) is 1x10-9 mol L-1.

Iron nitroprusside, Fe(II)NP was incorporated into a carbon paste electrode and the electrochemical studies were performed by cyclic voltammetry. The cyclic voltammogram of the modified electrode, Fe(II)NP showed two redox couples ( E½ox)1 = 0.24 and (E½ox)2 = 0.85 V vs. SCE attributed to Fe(II)/Fe(III) and Fe(II)(CN)5NO / Fe(III)(CN)5NO, respectively. The redox couple at (E½ox)1 = 0.24 V presents an electrocatalytic response for ascorbic acid. The modified paste electrode exhibits a decrease of 180 mV in the ascorbic acid oxidation. The modified graphite paste electrode gives a linear range from 1.0 × 10-3 to 2.6 × 10-2 mol L-1 of ascorbic acid with a detection limit of 1.4 × 10-3 (±1.2%) mol L-1 (n =3). The electrocatalytic oxidation of ascorbic acid compounds by the mediator has been used for the determination of ascorbic acid in a commercially pharmaceutical available product.

O Nitroprussiato de ferro, Fe(II)NP foi incorporado em um eletrodo de pasta de grafite, sendo os estudos eletroquímicos realizados empregando a técnica de voltametria cíclica. O voltamograma cíclico de Fe(II)NP exibiu dois pares redox com potencial formal (E0')1 = 0,24 e (E0')2 = 0,85 V vs. SCE atribuídos a Fe(II)/Fe(III) e Fe(II)(CN)5NO / Fe(III)(CN)5NO, respectivamente. O par redox com (E0')2 = 0,85 V apresentou uma resposta eletrocatalítica para os compostos sulfidrílicos; L-cisteína e N-acetylcisteína. A oxidação eletrocatalítica dos compostos sulfidrílicos pelo mediador foi empregada para a determinação de L-cisteína e N-acetilcisteína. O eletrodo de pasta de grafite modificado para a determinação de L-cisteína e N-acetilcisteína apresenta uma linearidade de 9,2 × 10-4 <FONT FACE=Symbol>-</FONT> 2,0 × 10-2 e 9,6 × 10-4 <FONT FACE=Symbol>-</FONT> 1,4 × 10-2 mol L-1 com limite de detecção de 1,9 ×10-4 mol L-1 e 1,5 × 10-4 mol L-1 e desvio padrão relativo de ± 5 e 4% (n=3) e sensibilidade amperométrica de 0,024 e 0,027 miA/mimol L-1. A aplicação deste eletrodo foi testada determinando-se N- acetilcisteína em um fármaco (Fluimucil).

Iron nitroprusside Fe(II)NP was incorporated into a carbon paste electrode and the electrochemical studies were performed with cyclic voltammetry. The cyclic voltammogram of Fe(II)NP exhibits two redox couple with formal potential (E0')1 = 0.24 e (E0')2 = 0.85 V vs SCE attributed to Fe(II)/Fe(II) and Fe(II)(CN)5NO / Fe(III)(CN)5NO, respectively. The redox couple with (E0')2 = 0.85 V presents an electrocatalytic response for sulfhydryl compounds. The electrocatalytic oxidation of sulfhydryl compounds by the mediator has been used for the determination of L-cysteine and N-acetylcysteine. The modified graphite paste electrode gives a linear range from 9.2 ×10-4 <FONT FACE=Symbol>-</FONT> 2.0 ×10-2; 9.6 × 10-4 <FONT FACE=Symbol>-</FONT> 1.4 × 10-2mol L-1 for the determination of L-cysteine and N-acetylcysteine, respectively, with detection limit of 1.9 ×10-4 mol L-1; 1.5 × 10-4 mol L-1 and relative standard desviations ± 5% and 1.5 × 10-3 mol L-1 ± 4% (n=3). The amperometric sensitivities are 0.024 and 0.027 muA/mumol L-1 for L-cysteine and N-acetylcysteine, respectively. The application of this electrode was tested and a commercial pharmaceutical product (Fluimucil) has been determined.

Sensores potenciométricos, amperométricos e condutométricos são sensores eletroquímicos com imensa aplicação nas áreas de meio ambiente, indústria e análises clínicas. O presente trabalho apresenta uma revisão generalizada dos aspectos fundamentais, os desenvolvimento e a contribuição destes sensores na área de química analítica, e reporta alguns aspectos relevantes dos avanços na área de sensores eletroquímicos no Brasil.

Potentiometric, amperometric and conductometric electrochemical sensors have found a number of interesting applications in the areas of environmental, industrial, and clinical analyses. This review presents a general overview of the three main types of electrochemical sensors, describing fundamental aspects, developments and their contribution to the area of analytical chemistry, relating relevant aspects of the development of electrochemical sensors in Brazil.

Miconazol é reduzido no eletrodo de mercúrio em valor de pH acima de 6,0 envolvendo formação de composto organometálico, responsável por um comportamento polarográfico anômalo. O processo eletródico apresenta uma larga contribuição de efeitos de adsorção. A droga pode ser determinada por voltametria de redissolução catódica de 8, 0 x 10-8 a 1, 5 x 10-6 mol L-1 em tampão Britton-Robinson pH 8,0 quando pré-acumulada por 30s em potencial de acúmulo de 0V. Um desvio padrão relativo de 3,8% foi obtido de 10 medidas de 1, 0 x 10-7 mol L-1 de miconazol em tampão B-R pH 8,0 e um limite de detecção de 1, 7 x 10-8 mol L-1 foi determinado usando 60s de tempo de deposição e velocidade de varredura de 100 mV s-1. O método proposto é simples, preciso e foi aplicado com sucesso para a determinação de miconazol na forma pura e em formulações comerciais, mostrando médias de recuperação de 99, 7 - 98, 4%.

Miconazole is reduced at mercury electrode above pH 6 involving organometallic compound formation, responsible for an anomalous polarographic behavior. The electrodic process presents a large contribution of the adsorption effects. The drug can be determined by cathodic stripping voltammetry from 8.0 x 10-8 to 1, 5 x 10-6 molL-1 in Britton-Robinson buffer pH 8.0, when pre-accumulated for 30s at an accumulation potential of 0V. A relative standard deviation of 3.8% was obtained for ten measurements of 1.0 x 10-7 molL-1 miconazole in B-R buffer pH 8.0 and a limit detection of 1, 7 x 10-8 molL-1 was determined using 60s of deposition time and scan rate of 100 mVs-1. The proposed method is simple, precise and it was applied successfully for the determination of the miconazole in pure form and in commercial formulations, showing mean recoveries of 99.7-98.4%.

Clotrimazol é reduzido em eletrodo de mercúrio em tampão fosfato pH > 6 através de um processo reversível de um elétron. O processo eletródico apresenta forte efeito de adsorção, o qual pode ser minimizado na presença de Triton X-100. Clotrimazol pode ser determinado em níveis de 50 ng mL-1 quando pré-acumulado durante 3 min à -0,20 V. O método proposto foi aplicado para determinação do fármaco em formulação comercial.

The reduction of clotrimazole at a mercury electrode, in phosphate buffer, pH>6, involves a reversible one-electron process. The electrochemical process presents a large contribution from adsorption effects. For the differential pulse polarographic determination the addition of Triton X-100 is recommended. Clotrimazole can be determined by cathodic stripping voltammetry at 50 ng mL-1 level when pre-accumulated for 3 min at an accumulation potential of -0.20 V. The proposed method is applied successfully for the determination of clotrimazole in a commercial formulation.