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

Abstract

Two simple sensitive and cost-effective spectrophotometric methods are described for
the determination of lansoprazole (LPZ) in bulk drug and in capsules using ceric ammonium
sulphate (CAS), iron (II), orthophenanthroline and thiocyanate as reagents. In both methods, an
acidic solution of lansoprazole is treated with a measured excess of CAS followed by the
determination of unreacted oxidant by two procedures involving different reaction schemes. The
first method involves the reduction of residual oxidant by a known amount 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 second 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
amount CAS reacted corresponds to the amount of LPZ. In method A, the absorbance is found to
increase linearly with the concentration of LPZ where as in method B a linear decrease in
absorbance occurs.