Este artigo descreve o desenvolvimento e a aplicação de um dispositivo portátil, simples e barato para a determinação colorimétrica quantitativa de fármacos em formulações farmacêuticas. O sensor é um resistor detector de luz (RDL) colocado numa célula de PTFE e acoplado a um multímetro de baixo custo. Os estudos quantitativos foram realizados utilizando captopril/p-cloranil/H2O2 e metildopa/molibdato de amônio como sistemas reacionais. As curvas de calibração foram obtidas através da representação gráfica da resistência elétrica do RDL contra a concentração dos complexos coloridos formados nas faixas de 1,84 × 10-4 e 1,29 × 10-3 mol L-1 e 5,04 × 10-4 e 2,52 × 10- 3 mol L-1 para captopril/p-cloranil/H2O2 e de metildopa/molibdato de amônio, respectivamente, com bons coeficientes de determinação. As análises estatísticas dos resultados obtidos mostraram que não houve diferença significativa entre os métodos propostos e os métodos oficiais como evidente a partir dos testes "t-Student" eF-Fisher, com nível de confiança de 95%. Os resultados deste estudo demonstram que o instrumento proposto neste trabalho é simples, de fácil operação, baixo custo e apresentou boa exatidão e boa precisão para o doseamento de fármacos em medicamentos.

This article describes the application and performance of an inexpensive, simple and portable device for colorimetric quantitative determination of drugs in pharmaceutical preparations. The sensor is a light detector resistor (LDR) incorporated into a black PTFE cell and coupled to a low-cost multimeter (Ohmmeter). Quantitative studies were performed with captopril/p-chloranil/H2O2 and methyldopa/ammonium molybdate systems. Calibration curves were obtained by plotting the electrical resistance of the LDR against the concentration of the colored species in the ranges 1.84 × 10-4 to 1.29 × 10-3mol L-1 and 5.04 × 10-4 to 2.52 × 10-3 mol L-1 for captopril/p-chloranil/H2O2 and methyldopa/ammonium molybdate systems, respectively, exhibiting good coefficients of determination. Statistical analysis of the results obtained showed no significant difference between the proposed methodologies and the official reported methods, as evidenced by the t-test and variance ratio at a 95% confidence level. The results of this study demonstrate the applicability of the instrument for simple, accurate, precise, fast,in situ and low-cost colorimetric analysis of drugs in pharmaceutical products.

A flow injection spectrophotometric procedure for the determination of glyphosate in commercial formulations of herbicides is proposed. The determination is based on the reaction of glyphosate and p-dimethylaminocinnamaldehyde, in acid medium, yielding a colored compound (l máx = 495 nm). Under optimal conditions, Beer's law is obeyed in a concentration range 40-640 mg mL-1 with a correlation coefficient of 0.9996. The detection limit was 8.60 mg mL-1 for glyphosate. The method was successfully applied for the determination of glyphosate in commercial formulations of herbicides. Recovery of glyphosate from various commercial samples of herbicides range from 91.0 to 110%.

This work proposes a sequential injection analysis (SIA) system for the spectrophotometric determination of norfloxacin (NOR) and ciprofloxacin (CIP) in pharmaceutical formulations. The methodology was based on the reaction of these drugs with p-(dimethylamino)cinnamaldehyde in micellar medium, producing orange colored products (λmax = 495 nm). Beer´s law was obeyed in the concentration range from 2.75x10-5 to 3.44x10-4 mol L-1 and 3.26x10-5 to 3.54x10-4 mol L-1 for NOR and CIP, respectively and sampling rate was 25 h-1. Commercial samples were analyzed and results obtained through the proposed method were in good agreement with those obtained using the reference procedure for a 95% confidence level.

A simple and more environmentally friendly method by combined spot test-diffuse reflectance spectroscopy for determining metoclopramide in pharmaceutical formulations is described. The method is based on the reaction between metoclopramide and p-dimethylaminocinnamaldehyde, in the presence of HCl, producing a colored compound (λmáx = 580 nm) on the filter paper. The linear range was from 5.65 x 10-4-6.21x10-3 mol L-1 (r = 0.999). The limit of detection was 1.27 x 10-4 mol L-1. The proposed reflectometric method was applied successfully to the determination of metoclopramide in pharmaceuticals and it was favorably compared with the Brazilian or British Pharmacopoeia methods at 95% confidence level.

This paper proposes a methodology for spectrophotometric determination of hexamethylenetetramine (HMT) by using chromotropic acid in a phosphoric acid media employing a domestic microwave oven as a source of heating. The reddish-purple soluble product is quantitatively formed after 30 s of irradiation and obeys the Beer´s law in the range between 0.1-1.2 mg L-1 HMT (r = 0.99925). The method was applied successfully in commercial pharmaceutical preparations containing dyes in their composition. The results showed that the method proposed is feasible for simplicity, speed, low cost, precision and accuracy when compared with United States Pharmacopeia official method.

This paper describes a simple and rapid spectrophotometric method for quantitative determination of sildenafil citrate based on its reaction with p-chloranil accelerated by hydrogen peroxide, producing a stable purple compound (λmax= 535 nm). In the absence of peroxide this reaction is very slow. The experimental conditions were optimized by using response surface methodologies. Beer's law is obeyed in a concentration range of 8.52 x 10-5 - 1.70 x 10-3 mol L-1 (r = 0.999). The detection limit was 1.96 x 10-5 mol L-1. The method was successfully applied for the determination of sildenafil citrate in medicines with good accuracy and precision.

No presente trabalho foi desenvolvido um método espectrofotométrico rápido, simples e seletivo para análise de ácido glicólico, o qual baseia-se na reação colorida entre o formaldeído liberado pelo ácido glicólico e o ácido cromotrópico, quando a reação é realizada em meio de ácido fosfórico concentrado e com aquecimento, utilizando para isso irradiação em forno de microondas doméstico para acelerar a reação. O composto corado formado apresenta um máximo de absorção a 570 nm, sendo necessários apenas 30 segundos de irradiação em forno de microondas (1100 Watts) para que a reação seja completa. A Lei de Beer é obedecida no intervalo de 0-2208 mg L-1. O método proposto foi aplicado na análise de amostras comerciais de ácido glicólico utilizadas em farmácias de manipulação no preparo de medicamentos de combate à acne, fornecendo bons resultados, com recobrimentos entre 97,0-101,4% e desvio padrão de 0,2-0,4%.

A rapid, simple and selective spectrophotometric for the determination of glycolic acid is proposed. This method is based on selective reaction between the formaldehyde splitted off by the glycolic acid, which reacts with chromotropic acid in a phosphoric acid medium, producing a violet-red compound (lambda max = 570 nm). The colored compound formation was accelerated by irradiating the reacting mixture with microwave energy for 30 seconds (1100 Watts). Beer's Law is obeyed in a concentration range of 0-2208 mg L-1. The proposed method was applied in the analysis of comercial samples of glycolic acid. Recoveries were within 97,0-101,4%, with standard deviations ranging from 0,2 to 0,4%.

O presente artigo descreve uma metodologia espectrofotométrica para a análise de paraformaldeído presente em amostras de saneantes comerciais e industriais, utilizando-se ácido cromotrópico (ACT), ácido clorídrico concentrado e peróxido de hidrogênio, produzindo um composto púrpura - avermelhado (lambda max = 575 nm). A lei de Beer é obedecida numa faixa de concentração de 0,8 - 4,8 mg L-1 em formaldeído, apresentando excelente coeficiente de correlação (r = 0,9999). Os valores obtidos nas análises concordaram muito favoravelmente com os obtidos pelo procedimento padrão recomendado pelo NIOSH (National Institute for Occupational Safety and Health).

This paper describes a spectrophotometric method for the paraformaldehyde analysis in industrial and commercial disinfectant samples using chromotropic acid, concentrated hydrochloridric acid and hydrogen peroxide. The reaction produces a violet-red compound (lambda max = 575 nm). The method permits the determination of paraformaldehyde over a concentration range of 0.8-4.8 mg L-1 and the results obtained by the proposed method compared very favorably with those obtained by NIOSH’s standard procedure.

No presente trabalho desenvolveu-se metodologia simplificada para análise de hexametilenotetramina em medicamentos que apresentam corantes em sua formulação (azul de metileno, Ponceau Red, Bordeaux Red, acriflavina) seguida por titulação ácido-base usando indicador. O método foi aplicado com sucesso a amostras comerciais e os resultados obtidos foram comparados com aqueles encontrados por titulação potenciométrica, apresentando muito boa concordância. Recobrimentos situaram-se na faixa de 101,3 - 104,2%, com desvios padrão de 0,1 - 2,1.

In the present work a simplified methodology for hexamethylenetetramine analysis in pharmaceutical formulations in the presence of dyes (methylene-blue, ponceau Red, bordeaux Red, acriflavine), followed by acid-base titration using indicators is proposed. The proposed method was applied to commercial samples and the analytical results obtained for these products compared favorably with the results obtained by means of potentiometric titration. Recoveries were within 101,3 - 104,2 %, with standard deviations ranging from 0,1 to 2,1%.

The oxidation process of sulfur (IV) species (SO2, HSO3- e SO32-) by oxygen, catalysed by trace metal ion and complexes, can play an important role in atmospheric, analytical and bioinorganic chemistry. An overview of the most important reactions in these fields is presented. A fascinating redox cycling of the metal ions and complexes during such autoxidation process was revealed by the combination of kinetics and coordination chemistry studies.