Validation of the spectrophotometric determination of omeprazole and pantoprazole sodium via their metal chelates.

Spectrophotometric procedures for the determination of two irriversible proton pump inhibitors, omeprazole (OMZ) and pantoprazole (PNZ) sodium have been developed, the procedures are based on the formation of 2:1 chelates of both drugs with different metal ions. Pantoprazole sodium is quantified by a stability-indicating procedure through chelation with iron (III) in aqueous-ethanol medium to form an orange chelate picked at 455 nm. The procedure retains its accuracy in presence of up to 70% of its degradate, sulfenic acid prepared by degrading the pure drug in borate buffer of pH 8 at 37 degrees C for 5 days. The colored chelates of OMZ in ethanol are determined spectrophotometrically at 411, 339 and 523 nm using iron (III), chromium (III) and cobalt (II), respectively. Regression analysis of Beer's plots showed good correlation in the concentration range of 15-95, 10-60 and 15-150 microml(-1) of pure OMZ using iron (III), chromium (III) and cobalt (II), respectively, and in the range of 30-300 microg ml(-1) of PNZ sodium using iron (III). The limits of detection are 0.22-3.65 microml(-1) while limits of quantitation range between 0.74 and 12.17 microg ml(-1). The optimum assay conditions are investigated and the recovery of the cited drugs from their dosage forms ranges from 97.2 to 100.3%. Good values of precision are obtained, intraday R.S.D. are 0.93-1.75% and the inter day R.S.D. are 0.51-3.29%.