Spectrophotometric determination of isoxsuprine hydrochloride using 3-methyl-2-benzothiazolinone hydrazone hydrochloride in spiked human urine and pharmaceuticals

Two selective and sensitive spectrophotometric methods are proposed for the determination of isoxsuprine hydrochloride (ISX) in spiked human urine and in pharmaceuticals. The methods are based on the oxidative-coupling reaction between 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) and ISX in the presence of Ce(SO4)2. The novelty of the proposed reaction is the formation of two different colored chromogens at two different pHs. The resulting product at pH < 1.5 is a red colored chromogen peaking at 500 nm (method A) and that formed between the pH 3.85 and 4.15, is violet colored with an absorption maximum at 580 nm (method B). In both the methods, absorbance of the chromogen is found to increase linearly with the concentration of ISX as is corroborated by the correlation coefficients of 0.9989 and 0.9970, and the systems obey Beer's law over the ranges of 1.4-21.0 and 1.0-15.0 μg ml−1, for method A and method B, respectively. The calculated molar absorptivities are 1.08 × 104 and 1.78 × 104 l mol−1 cm−1 for method A and method B, respectively with corresponding Sandell sensitivity values of 0.0311 and 0.0190 μg cm−2. The reaction stoichiometry, in both the methods, was evaluated by the limiting logarithmic method and was found to be 1:1 (ISX:MBTH). The methods were successfully applied to the determination of ISX in spiked human urine and pharmaceutical formulation.