Utilization of alizarin derivatives for the sensitive spectrophotometric determination of two proton pump inhibitors in pharmaceutical formulations

Simple, sensitive, selective and validated spectrophotometric methods were developed for the determination of two proton pump inhibitors namely, rabeprazole (RBZ) and pantoprazole (PNZ) using alizarin derivatives; quinalizarin (I), alizarin red S (II), alizarin (III) and alizarin yellow G (IV) as reagents. The reaction is based on the formation of charge transfer complexes between the studied drugs and the chromogenic reagents I, II, III and IV in methanolic medium which showed an absorption maximum at optimum wavelengths 552, 535, 531 and 417 nm for RAB and 553, 533, 525 and 403 nm for PNZ using I, II, III and IV, respectively. The optimization of the reaction conditions such as the type of solvent, reagent concentration and reaction time was investigated. Beer’s law is obeyed in the concentration ranges 0.5–16 and 0.5–12 μg ml^–1 for RAB and PNZ, respectively. The molar absorptivity, Sandell sensitivity, detection and quantification limits are also calculated. The correlation coefficient was ≥0.9991 (n = 6) with a relative standard deviation (R.S.D.) of ≤1.93. The methods are successfully applied to the determination of the studied drugs in pharmaceutical formulations without interference from excipients and additives and the validity assesses by applying the standard addition technique. Results obtained by the proposed methods for the pure drugs and commercial tablets agreed well with those obtained by the reported methods.