Beer's and lambert's laws in methyldopa analysis
Okoba, Siro A P
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A new, simple, precise, rapid, accurate 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 ions. Absorbance of this resulting yellow product compound is measured at 344nm. Beer's Law is obeyed in a concentration range of 50 - 200 IJg/ml methyldopa with an excellent coefficient (e = 3.478xlO-3 Imollcrn" and intercept zero). No interference was observed from common excipients in formulations. The results show a simple, fast, accurate 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 stated compositions as per the monographs referred to at 93.76% and 93.34% confidence levels. The complex formed was stable over a 60 minute time interval. The best molybdate ion concentration for the analysis was established at 1.0% vslv. The only drawback encountered was sample fluorescence at wavelengths below 320nm. The experiment was successful as evidenced by the results obtained. However, further research and trials of this method are recommended its proper validation and application. Keywords: methyldopa; spectrophotometric determination; pharmaceutical formulations; ammonium molybdate; absorbance.