Spectrophotometric determination of verapamil hydrochloride in drug formulations with chloramine-T as oxidant

A new spectrophotometric method is described for the determination of verapamil hydrochloride, based on its oxidation with chloramine-T in hydrochloric acid medium. It produces a yellow colored compound with maximum absorbance at 425 nm. Beer's law was obeyed in the concentration range 0-340 mug mL(-1) with molar absorptivity 2 x 10(3) L mol(-1) cm(-1) and RSD 0.3-0.82%. All variables were studied to optimize the reaction conditions. No interferences were observed from the common excipients present in the formulations. The method has been applied successfully to the determination of the drug in pharmaceutical preparations. Statistical comparison of the results with those from the reference method reveals excellent agreement and confirms that accuracy and precision are not significantly different.