Spectrophotometric Methods for Determination of Ritodrine in Bulk and in Pharmaceutical Dosage Forms

Three simple and sensitive spectrophotometric methods are described for determination of ritodrine hydrochloride (RTH) either in pure form or dosage forms. The first method was based on the reaction with 4-chloro-7-nitrobenzo-2-oxa-1, 3-diazole (NBD-Cl) in borate buffer of pH 8.0 producing a yellow colored product measured at 392 nm. The second and third methods were based on RTH oxidation with either 1, 10-phenanthroline or Folin-Ciocalteu reagents producing red and blue chromogens which were measured at 510 and 760 nm, respectively. Beer's law was obeyed in the ranges of, 2-16, 0.2-2, 0.8-12 μg/mL with the minimum detectable values of 0.1, 0.05, 0.14 μg/mL for the three methods, respectively. Different experimental parameters affecting the development and stability of colored products were carefully studied and optimized. The effect of different foreign matters and sensitizers on the color development in the three proposed methods was also studied. The proposed methods were successfully applied to the determination of RTH in its dosage forms. The obtained percentage recoveries were 99.73±0.72, 99.88±1.2, 99.97±0.42 for the three proposed methods, respectively. The obtained results were statistically validated and compared with those obtained with a reference method. Proposals of the reactions mechanisms were presented.