Abstract
An accurate, precise and simple flow injection quantitative method for the determination of a-methyldopa in pharmaceutical formulations is proposed. The method is based on the reaction between a-methyldopa and p-aminophenol in strong alkaline medium. The reaction product is determined spectrophotometrically at 608 nm. Five pharmaceutical preparations purchased in the local market were analyzed. The results were compared with those obtained with the spectrophotometric United States Pharmacopoeia method. The statistical Student's t-test was applied to compare the results obtained with the two independent methods. In all cases complete agreement was observed, in a confidence level of 95% (α=0.05). Considering five samples analyzed using the proposed method and three determinations for each sample, the observed mean relative standard deviation, RSD, is about 1.7 %. The working analytical range, considering the final solution, is between 2×10-4 mol L-1 and 3×10-3 mol L-1. The correlation coefficient R of the analytical quadratic curve is 0.99998. The detection limit is about 0.3×10-4 mol L-1 in the final solution introduced in the flow system (3×SD of the blank) and 48 determinations can be performed per hour.
