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A new composite electrode based on multiwall carbon nanotubes (MWCNT) and silicone-rubber (SR) was developed and applied to the determination of propranolol in pharmaceutical formulations. The effect of using MWCNT/ graphite mixtures in different proportions was also investigated. Cyclic voltammetry and electrochemical impedance spectroscopy were used for electrochemical characterization of different electrode compositions. Propranolol was determined using MWCNT/SR 70 % (m/m) electrodes with linear dynamic ranges up to 7.0 mmol L À1 by differential pulse and up to 5.4 mmol L À1 by square wave voltammetry, with LODs of 0.12 and 0.078 mmol L À1, respectively. Analysis of commercial samples agreed with that obtained by the official spectrophotometric method. The electrode is mechanically robust and presented reproducible results and a long useful life.

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O uso de um eletrodo compósito à base de grafite de borracha de silicone (GSR) na determinação de rutina, (vitamina P), por voltametria de pulso diferencial, é descrito. Voltamogramas cíclicos da rutina apresentaram um par de picos de oxidação/redução no GSR em 0,411 e 0,390 V (vs. ECS), respectivamente, em solução tampão Britton-Robinson (B-R) pH 4,0. Em voltametria de pulso diferencial (DPV), após a otimização das condições, o pico de oxidação em 0,370 V (vs. ECS) foi usado na determinação quantitativa de rutina. Neste caso, um intervalo linear entre 5,0-50,0×10 -8 mol L -1 foi observado com um limite de detecção de 1,8×10 -8 mol L -1 . Recuperações de 94 a 113% foram observadas. A superfície do eletrodo foi renovada por polimento, com uma repetibilidade de 1,09 ± 0,06 µA (n = 10) para a corrente de pico. A rutina foi determinada em uma formulação farmacêutica e os resultados concordaram com aqueles obtidos de um método oficial com 95% de confiança.The possibility of using a graphite silicone-rubber composite electrode (GSR) in a differential pulse voltammetric(DPV) procedure for rutin (vitamin P) determination is described. Cyclic voltammograms of rutin presented a reversible pair of oxidation/reduction peaks respectively at 0.411 and 0.390 V (vs. SCE) at the GSR surface in Britton-Robinson(B-R) buffer solution pH 4.0. In DPV after optimization of conditions, an oxidation peak at 0.370 V (vs. SCE) was used to quantitative determination of rutin in B-R buffer solution pH 4.0. In this case a linear dynamic range of 5.0×10 -8 to 50.0×10 -8 mol L -1 was observed with a detection limit of 1.8×10 -8 mol L -1 for the analyte. Recoveries from 94 to 113% were observed. The electrode surface was renewed by polishing after each determination, with a repeatability of 1.09 ± 0.06 µA (n = 10) peak current. Rutin was determined in a pharmaceutical formulation using the proposed electrode and the results agreed with those from an official method within 95% confidence level.

A multiwall carbon nanotube/silicone rubber (MWCNT/SR) composite electrode has been used for the determination of hydrochlorothiazide (HCTZ) in pharmaceutical formulations by differential pulse voltammetry (DPV). The electro-oxidation process was evaluated by cyclic voltammetry, from which it was observed that HCTZ presents an irreversible oxidation peak at 0.82 V vs. saturated calomel electrode (SCE) in the potential range from 0.5 to 1.1 V, in Britton-Robinson buffer pH 7.0 at MWCNT/SR. HCTZ was determined by DPV using a MWCNT/SR 70% (MWCNT, m/m) composite electrode after the optimization of the experimental parameters. The linear range was from 5.0 to 70.0 l mol L À1 , with a limit of detection (LOD) of 2.6 l mol L À1 . The HCTZ was determined in pharmaceutical formulations using the proposed composite electrode and the results agreed with those from the official high performance liquid chromatography (HPLC) method within 95% confidence level, according to the t-Student test.

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Recently, graphene nanoribbons (GNR) have gained prominence for applications in high performance electrodes. However, this material might present some complications, such as restacking formation, lower electron mobility due to oxygen-containing functionalities and non-reversible structural damages related to oxidation processes, decreasing GNR response. Several papers sought to minimize this limitation, but the most part use high cost materials, rendering ineffective or hard the application of this device. Less expensive alternatives have to show up, enabling a viable cost/performance ratio. In this sense, the aim of this study was to evaluate the performance of electrodes built from the incorporation of graphene oxide nanoribbons (O-GNR) in carbon paste electrodes (CPE), at different mass percentages (w/w), applied as high performance electrodes. O-GNR synthesis was made through an adaptation of the longitudinal unzipping of multiwalled carbon nanotubes method. Experimental results demonstrated that the simple dispersion of O-GNR in carbon paste electrodes is enough to enhance the response of this material, reaching a double layer capacitance as high as 350 mF cm −2 in 1.0 mol L −1 KCl solution. Scan rate up to 300 mV s −1 showed to disturb the double layer capacitance for all electrodes evaluated.