Wallans Torres Pio dos Santos

Simultaneous determination of caffeine, paracetamol, and ibuprofen in pharmaceutical formulations by high‐performance liquid chromatography with UV detection and by capillary electrophoresis with conductivity detection

Paracetamol, caffeine and ibuprofen are found in over-the-counter pharmaceutical formulations. In this work, we propose two new methods for simultaneous determination of paracetamol, caffeine and ibuprofen in pharmaceutical formulations. One method is based on high-performance liquid chromatography with diode-array detection and the other on capillary electrophoresis with capacitively coupled contactless conductivity detection. The separation by high-performance liquid chromatography with diode-array detection was achieved on a C18 column (250×4.6 mm(2), 5 μm) with a gradient mobile phase comprising 20-100% acetonitrile in 40 mmol L(-1) phosphate buffer pH 7.0. The separation by capillary electrophoresis with capacitively coupled contactless conductivity detection was achieved on a fused-silica capillary (40 cm length, 50 μm i.d.) using 10 mmol L(-1) 3,4-dimethoxycinnamate and 10 mmol L(-1) β-alanine with pH adjustment to 10.4 with lithium hydroxide as background electrolyte. The determination of all three pharmaceuticals was carried out in 9.6 min by liquid chromatography and in 2.2 min by capillary electrophoresis. Detection limits for caffeine, paracetamol and ibuprofen were 4.4, 0.7, and 3.4 μmol L(-1) by liquid chromatography and 39, 32, and 49 μmol L(-1) by capillary electrophoresis, respectively. Recovery values for spiked samples were between 92-107% for both proposed methods.

Simultaneous determination of paracetamol and ibuprofen in pharmaceutical samples by differential pulse voltammetry using a boron-doped diamond electrode

O presente trabalho apresenta uma metodologia simples, rapida e de baixo custo para determinacao simultânea de paracetamol (PC) e ibuprofeno (IB) em formulacoes farmaceuticas por voltametria de pulso diferencial usando eletrodo de diamante dopado com boro (BDD). Os analitos apresentaram picos de oxidacao definidos em 0,85 V para o PC e 1,72 V para o IB (vs. Ag/AgCl) sobre o eletrodo de trabalho de BDD em meio de uma solucao de H2SO4 0,1 mol L-1 com 10% (v/v) de etanol. As curvas de calibracao mostraram uma resposta linear para determinacao simultânea dos analitos entre 20 a 400 µmol L-1 (r2 = 0,999) e os limites de deteccao obtidos pelas regressoes foram de 7,1 µmol L-1 e 3,8 µmol L-1 para PC e IB, respectivamente. Os estudos de adicao e recuperacao nas amostras ficaram proximos de 100% e os resultados foram validados por metodos cromatograficos.

Simple flow injection amperometric system for simultaneous determination of dipyrone and paracetamol in pharmaceutical formulations

In this work a simple flow injection methodology with pulsed amperometric detection for simultaneous determination of dipyrone (DI) and paracetamol (PCT) in pharmaceutical formulations is described. The compounds are detected by applying four sequential potential pulses as function of the time. Dipyrone is directly detected at +0.40 V and paracetamol indirectly at 0.00 V through the reduction of the oxidation product (N-acetyl-p-benzoquinoneimine) electrochemically generated at +0.65 V. The fourth potential pulse (-0.05 V) is applied for the cleaning of the electrode surface (glassy carbon). The linear response range was optimized between 9 and 45 mg L-1 for dipyrone and 6 and 30 mg L-1 for paracetamol. Linear regression of these two series of experiments leads to excellent correlation coefficients (R = 0.999) for both analytes and recoveries of around 100%. The proposed methodology allows an analytical frequency of 45 injections h-1 with a consumption of 1.5 mL of solution per minute. The relative standard deviation for 24 successive injections of solutions containing DI and PCT was calculated as 0.4% and 0.2%, respectively. The developed methodology was successfully used for the determination of dipyrone and paracetamol in pharmaceutical samples.

Análise por injeção em fluxo com detecção amperométrica de múltiplos pulsos: potencialidades e aplicações

The potentialities and applications of the Multiple Pulse Amperometric detection (MPA) coupled with Flow Injection Analysis (FIA) are evaluated. Important aspects as cleaning and activation of electrode surface, indirect and simultaneous analysis of electroactive compounds and the use of the internal standard method for quantifications utilizing FIA-MPA are presented. The main parameters concerning the detection of electroactive analytes by multiple pulse amperometric detection in flowing solutions were also discussed. In addition, aspects such as flow rate, sample volume, application time of the potential pulses and instrumentation necessary for implementing of the method were also addressed.

Determinação de nimesulida por análise por injeção em fluxo com detecção amperométrica de múltiplos pulsos

A simple and fast method for the determination of nimesulide (NI) using flow injection analysis with multiple-pulse amperometric (FIA-MPA) detection at a boron-doped diamond (BDD) electrode was developed. The method was based mainly on the application of a four-potential waveform, E1(det) = -0.8 V / 30 ms, E2(det) = 0.6 V / 30 ms, E3(det) = -0.4 V / 30 ms and E4(cleaning) = -0.45 V / 300 ms versus Ag/AgCl (3.0 mol L-1 KCl). NI was detected at three different electrode potentials, at which the nitro group undergoes different redox reactions. The proposed method was selective and sensitive (detection limit of 81.0 nmol L-1), and successfully applied for the determination of NI in pharmaceutical formulations, yielding similar results to those obtained by the reference method.

Determination of Sildenafil Citrate (Viagra ® ) in Various Pharmaceutical Formulations by Flow Injection Analysis with Multiple Pulse Amperometric Detection

O presente trabalho apresenta uma metodologia simples, rapida e de baixo custo para a determinacao de citrato de sildenafila (SC) em formulacoes farmaceuticas de referencia (Viagra®) e em produtos similares, genericos e manipulados, por amperometria de multiplos pulsos em sistema FIA (analise por injecao em fluxo). O metodo consiste na aplicacao de tres pulsos de potencial (sequenciais) em funcao do tempo sobre um eletrodo de trabalho de diamante dopado com boro. SC foi detectado em 1,6 e 1,9 V por meio de dois diferentes processos irreversiveis de oxidacao. Um terceiro pulso de potencial (1,0 V) foi aplicado para regeneracao da superficie do eletrodo. Foram obtidos limites de deteccao na ordem de 10 nmol L-1 e desvio padrao relativo menor que 0,2% (n = 10) para SC 4,5 X 10-5 mol L-1, permitindo 86 injecoes por hora. Estudos de adicao e recuperacao nas amostras ficaram proximos de 100% e os resultados foram validados por cromatografia.

Uso da pressão gerada por uma coluna de água para controle da vazão em sistemas de análises em fluxo

This work presents a new approach to control the flow rate in hydrodynamic flow experiments. The combination of air pressure generated by an aquarium air pump and the pressure generated by a water column were used for this purpose. This device supports a stable flow rate without pulsation for a long period of time. Furthermore, the flow rate can be easily controlled at various values in one or more streams. The performance of this approach was investigated using Fe(CN)64- solutions in flowing systems using amperometric and voltammetric detection in wall-jet configuration. The results showed that the performance of the proposed device was better than a commercial peristaltic pump. It suggests that this approach can be used successfully in flow analysis systems.

Improved NADH Electroanalysis on Nickel(II) Phthalocyanine Tetrasulfonic Acid/ Calf Thymus Deoxyribonucleic Acid/Reduced Graphene Oxide Composite

This work describes the electrochemical performance of a novel composite based on nickel tetrasulfonated phthalocyanine (NiTsPc), deoxyribonucleic acid from calf thymus (CT-DNA) and reduced graphene oxide (rGO) for the electroanalysis of reduced β-nicotinamide adenine dinucleotide (NADH), through electrocatalytic oxidation. The modified electrode was denoted as CT-DNA/NiTsPc/rGO. Fourier transform infrared and ultraviolet-visible spectroscopies were performed to characterize the composite material. The electrochemical performance of the composite for NADH oxidation was investigated by cyclic voltammetry (CV), chronoamperometry and differential pulse voltammetry (DPV). The CT-DNA/NiTsPc/rGO modified glassy carbon electrode (GCE) showed an excellent electrocatalytic activity for NADH oxidation with apparent electrocatalytic rate constant (kobs) of 7.35 × 10 L mol s and linear response range for NADH from 1 up to 1350 μmol L for n = 12 (r = 0.999). The proposed sensor shows sensitivity, detection limit and quantification limit of 0.014 μA L mol, 0.3 and 1 μmol L, respectively. The prepared sensor was further tested for the determination of NADH in artificial human urine samples, showing promising biomedical applications.

Development of a Selective and Sensitive Sensor for Urate Determination Based on Tris(1,10-phenantroline)copper(II) Bis(tetracyanoquinodimethanide) Adsorbed on Carbon Nanotubes

The present work describes the development of a selective electrochemical sensor for urate based on tris(1,10-phenantroline)copper(II) bis(tetracyanoquinodimethanide) (Cu(phen)3(TCNQ)2) adsorbed on multi-walled carbon nanotubes (CNT). The composite material was characterized by infrared spectroscopy, scanning electron microscopy, and electrochemical impedance spectroscopy. The composite material showed an excellent electrocatalytic activity toward oxidation of urate. The heterogeneous charge transfer rate constant (k’) between the analyte and the sensor was determined using linear sweep voltammetry experiments. The composite material shows a linear range from 5 up to 2500 µmol L-1 with limit of detection of 1.05 µmol L-1 and limit of quantification of 3.50 µmol L-1. The high sensitivity and selectivity of the sensor for urate was sufficient for its determination in biological fluids. Finally, the proposed sensor was successfully applied in urine samples.

Efficient Enzyme-Free Biomimetic Sensors for Natural Phenol Detection.

The development of sensors and biosensors based on copper enzymes and/or copper oxides for phenol sensing is disclosed in this work. The electrochemical properties were studied by cyclic and differential pulse voltammetry using standard solutions of potassium ferrocyanide, phosphate/acetate buffers and representative natural phenols in a wide pH range (3.0 to 9.0). Among the natural phenols herein investigated, the highest sensitivity was observed for rutin, a powerful antioxidant widespread in functional foods and ubiquitous in the plant kingdom. The calibration curve for rutin performed at optimum pH (7.0) was linear in a broad concentration range, 1 to 120 µM (r = 0.99), showing detection limits of 0.4 µM. The optimized biomimetic sensor was also applied in total phenol determination in natural samples, exhibiting higher stability and sensitivity as well as distinct selectivity for antioxidant compounds.