Sensitive spectrophotometric determination of lansoprazole in pharmaceuticals using ceric ammonium sulphate based on redox and complex formation reactions.

摘要

Two simple sensitive and cost-effective spectrophotometric methods are described for the detn. of lansoprazole (LPZ) in bulk drug and in capsules using ceric ammonium sulfate (CAS), iron(II), orthophenanthroline and thiocyanate as reagents. In both methods, an acidic soln. of lansoprazole is treated with a measured excess of CAS followed by the detn. of unreacted oxidant by 2 procedures involving different reaction schemes. The 1st method involves the redn. of residual oxidant by a known amt. of iron(II), and the unreacted iron(II) is complexed with orthophenanthroline at a raised pH, and the absorbance of the resulting complex measured at 510 nm (method A). In the 2nd method, the unreacted CAS is reduced by excess of iron(II), and the resulting iron(III) is complexed with thiocyanate in the acid medium and the absorbance of the complex measured at 470 nm (method B). In both methods, the amt. CAS reacted corresponds to the amt. of LPZ. In method A, the absorbance is found to increase linearly with the concn. of LPZ where as in method B a linear decrease in absorbance occurs. The systems obey Beer's law for 2.5-30 and 2.5-25 μg mL-1 for method A and method B, resp., and the corresponding molar absorptivity values are 8.1 × 103 and 1.5 × 104 L mol-1cm-1. The methods were successfully applied to the detn. of LPZ in capsules and the results tallied well with the label claim. No interference was obsd. from the concomitant substances normally added to capsules. [on SciFinder(R)]