چکیده (انگلیسی):

A new, simple and low cost spectrophotometric method for the determination of methyldopa
in pharmaceutical preparations was developed. The method was based on the coupling of
methyldopa with 2,6-dichloroquinone-4-chlorimide (DCQ). The absorbance maximum (kmax) of
the resulted colored product was at 400 nm. Different buffers were used to determine the optimal
pH for the reaction. About 1% w/v acetate buffer with pH 8.0 gave the optimal pH required for
the reaction. Of the different solvents tried, water and ethanol were found to be the most suitable
solvents. Beer’s law was obeyed in concentration range of 4–20 lg/ml methyldopa. The correlation
coefficient was found to be (r = 0.9975). The limit of detection and limit of quantification were
1.1 lg/ml and 3.21 lg/ml, respectively. The reaction ratio between methyldopa and DCQ was studied
and found to be 1:3. The work included the study of the possible interference of hydrochlorothiazide
found in combination with methyldopa tablets. The method was validated and results
obtained for the assay of two different brands of methyldopa tablets were compared with the BP
method (colorimetric). The repeatability and reproducibility of the developed method were evaluated
and the obtained results quoted. The derivative formed as a result of the reaction of methyldopa
with DCQ was isolated and its possible mechanistic pathway was suggested.