Colorimetric assay of methyldopa bulk drug and tablets as its Fe(III) complex

A new colorimetric method for the determination of methyldopa is described. The method is based on the reaction of methyldopa with ferric chloride in the pH range of 3.0-3.5 and producing a water soluble (1:2) brown complex with maximum absorbance at 423 nm. The conditional stability constant of the complex at the optimum pH 3.0 and ionic strength 0.4 M, is found to be 10(7.5). Beer's low is obeyed up to 6 mmol/l methyldopa concentration. The RSD of the method is 0.708-1.226%. The proposed method was found to be suitable for the accurate and reproducible analysis of methyldopa bulk drug and tablets which is pointed by high recovery values 99.20-99.79%.