Abstract
A new, simple, precise, rapid and low-cost spectrophotometric method for methyldopa determination in pharmaceutical preparations is described. This method is based on the complexation reaction of methyldopa with molybdate. Absorbance of the resulting yellow coloured product is measured at 410 nm. Beer's Law is obeyed in a concentration range of 50 - 200 µg ml-1 methyldopa with an excellent correlation coefficient (r = 0.9999). No interference was observed from common excipients in formulations. The results show a simple, accurate, fast and readily applied method to the determination of methyldopa in pharmaceutical products. The analytical results obtained for these products by the proposed method are in agreement with those of the Brazilian Pharmacopoeia procedure at 95% confidence level.
Highlights
Methyldopa (MTD), chemically known as α-methyl-3,4-dihydroxyphenylalanine (Figure 1), is a catechol derivative widely used as an antihypertensive agent
The proposed method involves the reaction of MTD with molybdate ions to produce a coloured water soluble complex
The absorption spectrum of the reaction product shows that the best analytical wavelength is located at 410 nm
Summary
Methyldopa (MTD), chemically known as α-methyl-3,4-dihydroxyphenylalanine (Figure 1), is a catechol derivative (catecholamine) widely used as an antihypertensive agent. Several types of analytical procedures have been employed for the analysis of catechol derivatives in pharmaceuticals formulations and/or biological specimens. These procedures include titrimetric determination [2,3,4,5,6,7], fluorimetry [8], kinetic methods [9], amperometry [10], gas chromatography [11, 12], high-performance liquid chromatography (HPLC) [13, 14], chemiluminescence [15, 16] and voltammetric determination [17]. The official method reported in USP [2] describes a nonaqueous titration for the assay of MTD
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