The independent determination of two beta-blocker agents, namely propranolol (PROP) and atenolol (ATN), in pharmaceutical formulations using square-wave voltammetry and a cathodically pretreated boron-doped diamond electrode is described. These electroanalytical determinations of propranolol or atenolol were carried out in 0.1molL(-1) H(2)SO(4) or 0.5molL(-1) NaNO(3) (pH 1.0, adjusted with concentrated HNO(3)), respectively. Excellent linear calibration curves, ranging from 0.20 to 9.0micromolL(-1) for PROP and from 2.0 to 41micromolL(-1) for ATN, with detection limits of 0.18 and 0.93micromolL(-1), respectively, were obtained. The obtained recoveries range from 93.9% to 105.0%, for PROP, and from 92.5% to 106.0%, for ATN. The proposed method was successfully applied in the determination of both beta-blockers in several pharmaceutical formulations (tablets), with results in close agreement at a 95% confidence level with those obtained using official spectrophotometric methods.

An electroanalytical method for the simultaneous determination of paracetamol (PAR), caffeine (CAF), and orphenadrine (ORPH) using the square‐wave voltammetry (SWV) and a cathodically pretreated boron‐doped diamond electrode was developed. The method exhibits linear responses to PAR, CAF, and ORPH in the concentration ranges 5.4×10−7–6.1×10−5 M, 7.8×10−7–3.5×10−5 M, and 7.8×10−7–3.5×10−5 M, respectively, with detection limits of 2.3×10−7 M, 9.6×10−8 M, and 8.4×10−8 M, respectively. The proposed method was successfully applied in the simultaneous determination of these analytes in pharmaceutical formulations.

Neste trabalho descreve-se a determinação do ácido acetilsalicílico (ASA) em formulações farmacêuticas empregando voltametria de onda quadrada (SWV) e um eletrodo de diamante dopado com boro (BDD). Neste método, ASA é determinado diretamente em solução de H 2 SO 4 0,01 mol L -1 , sem a necessidade da hidrólise alcalina. Foi obtido um único pico de oxidação no potencial de 1,97 V vs. Ag/AgCl (KCl 3,0 mol L -1 ) com características de uma reação irreversível. A curva analítica obtida é linear na faixa de concentração ASA de 2,50 × 10 -6 -1,05 × 10 -4 mol L -1 , com um limite de detecção de 2,0 µmol L -1 . O desvio padrão relativo foi menor que 1,4% para uma solução de ASA 45 µmol L -1 (n = 10). O método proposto foi aplicado com sucesso para a determinação de ASA em várias formulações farmacêuticas e os resultados obtidos foram concordantes com um método oficial da Farmacopéia Britânica, a um nível de confiança de 95%.In this paper the determination of acetylsalicylic acid (ASA) in pharmaceutical formulations using square-wave voltammetry (SWV) and a boron-doped diamond electrode (BDD) is described. By this proposed method, ASA is directly determined in a 0.01 mol L -1 H 2 SO 4 solution without the need of a previous time-consuming alkaline hydrolysis step. A single oxidation peak at a potential of 1.97 V vs. Ag/AgCl (3.0 mol L -1 KCl) with the characteristics of an irreversible reaction was obtained. The obtained analytical curve is linear in the ASA concentration range 2.50 × 10 -6 -1.05 × 10 -4 mol L -1 , with a detection limit of 2.0 µmol L -1 . The obtained relative standard deviation was smaller than 1.4% for a 45 µmol L -1 ASA solution (n = 10). The proposed method was applied with success in the determination of ASA in several pharmaceutical formulations; the obtained results were in close agreement, at a 95% confidence level, with those obtained using an official method of the British Pharmacopoeia.Keywords: acetylsalicylic acid determination, boron-doped diamond electrode, square-wave voltammetry, pharmaceutical formulations IntroductionAcetylsalicylic acid (ASA), shown in Figure 1, more popularly known as aspirin, is one of the oldest medicines that still plays an important role in modern therapeutics. It is widely employed in pharmaceutical formulations for the relief of headaches, fever, muscular pain, and inflammation due to arthritis or injury. It was first synthesized in 1897, by Felix Hoffmann, in the Farbenfabrik Freidrich Bayer laboratories, in Elberfeld, Germany. 1,2 The high consumption of this substance all over the world 3,4 indicates the importance of the development of new analytical methods to assess not only the quality but also the authenticity of the product.The rate of decomposition of ASA to salicylic acid (SA) and acetic acid (AA) is dependent on solution pH and temperature. In the pH range 11-12 ASA is quickly hydrolyzed, in the pH range 4-8 its hydrolysis rate is slow, and maximum stability is attained at pH 2-3. 5 Commonly, ASA is indirectly determined after its conversion to SA ...

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The determination of sildenafil citrate using differential pulse voltammetry and a cathodically pre-treated boron-doped diamond electrode is described. The obtained analytical curve is linear in the sildenafil concentration range 7.3 Â 10 À7 À 7.3 Â 10 À6 mol L À1 in a 0.1 mol L À1 H 2 SO 4 , with a detection limit of 6.4 Â 10 À7 mol L À1 . The proposed method, which is fast and simple to carry out, was successfully applied in the determination of sildenafil citrate in Viagra 1 pharmaceutical formulations, with results in close agreement (at 95% confidence level) with those obtained using a comparative HPLC method.

The modification of a glassy carbon electrode with multi-walled carbon nanotubes and gold nanoparticles within a poly(allylamine hydrochloride) film for the development of a biosensor is proposed. This approach provides an efficient method used to immobilize polyphenol oxidase (PPO) obtained from the crude extract of sweet potato (Ipomoea batatas (L.) Lam.). The principle of the analytical method is based on the inhibitory effect of sulfite on the activity of PPO, in the reduction reaction of o-quinone to catechol and/or the reaction of o-quinone with sulfite. Under the optimum experimental conditions using the differential pulse voltammetry technique, the analytical curve obtained was linear in the concentration of sulfite in the range from 0.5 to 22 μmol L(-1) with a detection limit of 0.4 μmol L(-1). The biosensor was applied for the determination of sulfite in white and red wine samples with results in close agreement with those results obtained using a reference iodometric method (at a 95% confidence level).