Determination of methyldopa in pharmaceutical formulations by combined spot test-diffuse reflectance spectroscopy

Abstract

Este trabalho descreve um método simples e rápido por "spot test" quantitativo, utilizando a espectroscopia de reflectância difusa para determinação de metildopa em formulações farmacêuticas. O método proposto baseia-se na reação de complexação entre metildopa e íons molibdato, formando um complexo amarelo na superfície do papel de filtro. As medidas de reflectância foram realizadas a 410 nm. A curva analítica obtida a partir do gráfico de densidade óptica do sinal de reflectância (A R ) vs. log da concentração de metildopa apresentou linearidade na faixa de 6,30 × 10 -3 a 1,89 × 10 -2 mol L -1 , com um coeficiente de correlação de 0,998. O limite de detecção foi de 2,74 × 10 -3 mol L -1 (R.S.D. = 1,02%). As substâncias comumente utilizadas como excipientes nas formulações farmacêuticas não interferem no método proposto. O método foi aplicado para a determinação de metildopa em formulações farmacêuticas comerciais. Os resultados obtidos por este método foram comparados favoravelmente com aqueles obtidos pelo método oficial, com 95% de nível de confiança. This paper describes a very simple and rapid quantitative reflectance spot test procedure for the determination of methyldopa in pharmaceutical formulations. This method is based on the complexation reaction of methyldopa with molybdate ions yielding a yellow stable complex on filter paper. Reflectance measurements were carried out at 410 nm. Under optimal conditions, the calibration graphs obtained for methyldopa by plotting the optical density of the reflectance signal (A R ) vs. the log of the concentration were linear from 6.30 × 10 -3 to 1.89 × 10 -2 mol L -1 , with a correlation coefficient of 0.998. The detection limit was 2.74 × 10 -3 mol L -1 (R.S.D. = 1.02%) for methyldopa. The common excipients used as additives in pharmaceuticals do not interfere in the proposed method. The method was applied to determine metyldopa in commercial pharmaceutical formulations. The results obtained by the proposed method compare favorably with those obtained by an official procedure at 95% confidence level. Keywords: methyldopa, diffuse reflectance, pharmaceuticals formulations IntroductionMethyldopa (α-methyl-3,4-dihydroxyphenylalanine, MTD) is a catechol derivative (catecholamine) widely used as antihypertensive agent. The MTD is a centrally acting alpha 2 -adrenoreceptor agonist, which reduces sympathetic tone and produces a fall in blood pressure. In recent years more and more strict regulations related to the quality control of pharmaceuticals led to increasing demands on the simplicity and rapidity of analytical assay. 34,35 Considering the simplicity of the spot test method, the use of small quantities of chemicals, the confidence and the rapidity of such kind of procedure, the quantitative spot-test analysis by diffuse reflectance spectroscopy could be interesting to develop analytical procedures for routine analysis of drugs in pharmaceuticals formulations. 675 Vol. 17, No. 4, 2006 For many years, the use of reflectance spectroscopy as an analytical techni...

Development and application of a portable instrument for drugs analysis in pharmaceutical preparations

“…Of the techniques used in several procedures most are based on kinetic measurements (James;Hoo;William, 2006), highperformance liquid chromatography (Bahrami, Kiani, Mirzaeei, 2006;Muzzi et al, 2008;Li et al, 2010), voltammetry (Rezaei, Askarpour, Ensafi, 2013), spectrophotometry (Gadkariem et al, 2009;Brasil, 2010;Matos,Silva;Ribeiro, 2012; and diffuse reflectance spectroscopy (Ribeiro, Pezza, Pezza, 2006).…”

Differential pulse voltammetric determination of methyldopa using MWCNTs modified glassy carbon decorated with NiFe2O4 nanoparticles

“…Methyldopa is a competitive inhibitor of dopadecarboxylase, which metabolized Ldopa into dopamine [3,4]. Many analytical methods have been reported for determination of catecholamine drugs, such as methyldopa, in biological samples including spectrophotometry [5][6][7][8], fluorescence [9,10], high-performance liquid chromatography [11][12][13], chemiluminescence [14][15][16], gas chromatography [17], and potentiometry [18]. Some of these methods described above have disadvantages such as low sensitivity, long analysis times, and/or require expensive instruments.…”

Quantitative Spot-Test Analysis of Metformin in Pharmaceutical Preparations Using Ultraviolet-Visible Diffuse Reflectance Spectroscopy

“…[21][22][23][24][25] In the last twelve years, some successful quantitative spot-test reflectance procedures have been related, for inorganic and organic analytes, including the development of simple reflectometric equipment. [21][22][23][26][27][28][29][30][31][32][33][34][35][36][37] In the present work, a simple and reliable method based on UV-visible diffuse reflectance was developed for the determination of metformin hydrochloride in pharmaceutical preparations after reaction of this substance with Ni…”