Felipe Silva Semaan

Electrochemical Behavior of Verapamil at Graphite-Polyurethane Composite Electrodes: Determination of Release Profiles in Pharmaceutical Samples

Abstract A solid graphite–polyurethane composite electrode has been used to determine release profiles of verapamil, a calcium-channel blocker. The electro-oxidation process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy and showed no adsorption of analyte or oxidation products, unlike at other carbon-based electrodes. Quantification gave linear ranges up to 40 µmol L−1 with cyclic voltammetry and detection limits of 0.7 µmol L−1 by differential pulse and square-wave voltammetry. Commercial product samples were successfully analyzed with results equal to those from spectrophotometry. Because no electrode surface renewal is needed, this electrode material has many advantages.

Spectrophotometric Determination of Furosemide Based on Its Complexation with Fe(III) in Ethanolic Medium Using a Flow Injection Procedure

Abstract A fast flow injection procedure with spectrophotometric detection based on the furosemide complexation with Fe(III) ions in ethanolic media is described. As carrier the flow single line system configuration used an ethanolic 10−2 mol L−1 Fe(III) solution flowing at 1.0 mL min−1, a 50 cm sample loop (250 µL total sample injection), and a 50 cm long reactor coil, at room temperature. The detection at 513 nm presented a linear dynamic range from 1.00×10−4 to 1.00×10−2 mol L−1, obeying the linear equation Abs=8.9×10−3+22.3×[furosemide] (r=0.998, n=7). The limit of detection (3σ/slope) was 3.00×10−5 mol L−1. The proposed method was applied to four commercial samples from different suppliers, as tablets and ampoules, and a synthetic urine sample spiked with the analyte without an effect from the other substances present in the formulation. The proposed procedure presented an analytical frequency of 95 measurements per hour. The results agreed with those from both the label and those determined by a spectrophotometric comparative procedure. Recoveries close to 100% were found in the commercial formulations and synthetic urine matrixes.

Rapid HPLC‐DAD Determination of Furosemide in Tablets Using a Short Home‐Made Column

Abstract Furosemide is a loop diuretic widely used as an antihypertensive. Its analysis, in pharmaceutical formulations, is often required for quality control and to develop new formulations. The aim of this work is to describe the development of a fast chromatographic procedure to determine furosemide in tablets. Adequate sample masses were prepared by dissolution of furosemide in ethanol with the aid of an ultrasonic bath, followed by filtration. After dilution, an aliquot was injected into the chromatographic system. The separations were obtained in a C18 home‐made column (50×4.6 mm, 3 µm) with methanol:phosphate buffer (10 mmol L−1, pH 5.5) (30∶70) as the mobile phase, at a flow rate of 1.0 mL min−1. A photodiode array detector (DAD) monitored signals between 190 and 380 nm, with special attention to 237 nm. The findings were 1.4%–6.2% intra‐assay precision; 1.6%–6.1% interassay precision (day and operator); recoveries of 90.2%, 97.5%, and 109.2% at 90%, 100%, and 110% concentration levels, respectively. The total chromatographic run lasted 3 minutes. By means of peak purity, obtained using the DAD, no interference of concomitants was observed. The residual graphic demonstrates the adequate linearity of the studied concentration interval. The proposed method was applied to commercial samples and shown to be less time and solvent consuming than the procedures previously reported in the literature.

Fast determination of minoxidil by photometric flow titration

A photometric flow titration based on the redox reaction between KMnO 4 and minoxidil is described. The best titration results were observed at 3.20 x 10 -4 mol L -1 KMnO 4 and 1.00 x 10 -3 mol L -1 minoxidil, using the minoxidil solutions as titrant. The flow rate was fixed at 17 mL min -1 and the titrant was added to the system in aliquots of 500 µL, the color changes were monitored at 550 nm. The method was applied to commercial samples and compared with the results from a chromatographic procedure. Recoveries from 97.6 to 102.8 % were observed depending on the sample. Comparison with the chromatographic procedure reveled relative errors of 3.5 - 4.0 %.

Flow‐Based Fluorimetric Determination of Furosemide in Pharmaceutical Formulations and Biological Samples: Use of Micelar Media to Improve Sensitivity

Abstract Two fast flow injection procedures with fluorimetric detection based on the furosemide emission are presented. The first configuration used a phosphate buffer solution pH 3.00, 0.2 ionic strength (μ) solution flowing at 3.0 ml min−1 as carrier, a 80 cm sample loop (400 µl total sample injection), and a 40 cm long reactor coil, which was kept at room temperature; the second has a unique difference: the introduction of a new channel of surfactant solution with reduction of flow rate. The excitation and emission were carried out at 270 and 410 nm, respectively; both systems presented linear dynamic range from 1.0×10−7 to 1.0×10−5 mol l−1. The limit of detection (3σ/slope) was 3.0×10−8 mol l−1, to the first system, and 10−8 mol l−1 for the second one. Both proposed methods were applied to three commercial samples from different suppliers, as tablets and ampoules, and a synthetic urine sample spiked with the analyte. They presented an analytical frequency of 90 and 60 measurements per hour, respectively to phosphate and micelar media. The results agreed with those from the label and determined by a UV‐Vis spectrophotometric comparative procedure. Recoveries around 101% were found in the commercial formulations and synthetic urine matrixes.

Cost-effective composite electrode for the fast voltammetric screening and determination of riboflavin (B2) and pyridoxine (B6) in pharmaceuticals

Universidade Federal Fluminense Instituto de Quimica Departamento de Quimica Analitica, Rua Outeiro Sao Joao Batista s/n, CEP 2402-150, Niteroi-RJ

Determination of Minoxidil by Bleaching the Permanganate Carrier Solution in a Flow-Based Spectrophotometric System

The determination of minoxidil (MX) with potassium permanganate as a carrier in a flow injection method is described. The detection at 550 nm was linear from 1.0 × 10−5 to 5.0 × 10−4 mol L−1. The limit of detection (3σ/slope) was 8.92 × 10−6 mol L−1, with an analytical frequency of 32 h−1. The proposed method was applied to commercial samples, with recoveries from 104.7 to 106.4%. Comparison with the HPLC procedure reveled relative errors from 0.48 to 1.4%, and the results agreed within a 95% confidence level.