Development and Validation of Spectrophotometric Method for the Determination of Lansoprazole in Bulk and Pharmaceutical Formulation through Ion-Pair Complex Formation Using Bromocresol Green

A simple, accurate, sensitive and reliable direct Spectrophotometric method have been developed, for the determination of Lansoprazole (LPZ) either in pure form or in pharmaceutical formulations by complex formation with Bromocresol Green (BCG). The method is based on the interaction of LPZ in dichloromethane (DCM) medium with acidic sulfonephthalein dye, namely, bromocresol green (BCG) to form stable, yellowcolored, ion-pair complex peaking at 417 nm. The variables were studied in order to optimize the reaction conditions. Beer's law was obeyed in the concentration range of 0.250-20.00 μg.mL^-1 with good correlation coefficient (R²= 0.9999). The relative standard deviation did not exceed 3.97%. The limit of detection (LOD) and the limit of quantification (LOQ) were 0.033 and 0.101 μg.mL^-1, respectively. The molar absorptivity was calculated to be 2.3068×10⁴ L.mol^-1.cm^-1. The composition of the ion-pair complex was found to be 1:1 by Job's method of continuous variations and the conditional stability constant (β) of the complex has been calculated. The proposed method was successfully applied to the analysis of Lansoprazole either in pure form or in pharmaceutical formulations with good accuracy and precision. The results obtained by the proposed method were compared favorably with those of the reference method.