A novel solid-contact sensor for flow injection determination of verapamil in pharmaceutical formulations and urine

A novel coated-graphite selective sensor based on verapamil ion pair with phosphomolybdate (PM) for its flow injection potentiometric (FIP) determination has been described. The sensor was prepared by coating the membrane cocktail containing PVC, plasticizer, and carrier on the surface of graphite rode. Influences of the membrane composition, pH, ions and possible interfering anions on the response properties of the electrode were investigated. The sensor membrane containing 3.6 % Ver-PM ion-pair and 62.0 % dioctylphethalate (DOP) in PVC possesses the best response with quasi-Nernstian slope of 62.6 mV/ decade over a wide concentration range of 6x10(-6)- 1x10(-2) M and a lower limit of detection (LDL) of 1.9 x 10(-6) M. The developed sensor has been applied for FIP determination of verapamil hydrochloride in pure solution, pharmaceutical preparations and urine. The parameters which control the FIP method have been optimized. The determination of verapamil assay in Verpamil tablets after shelf-storage for more than one year using the proposed sensor has been achieved. The percent of verapamil hydrochloride in tablets was found to decrease as the storage time increases and it reached a value of 73.5 % of its nominal value after 14 months storage.