Titrimetric and Spectrophotometric Methods for the Assay of Ketotifen Using Cerium(IV) and Two Reagents

One titrimetric and two spectrophotometric methods are described for the determination of ketotifen fumarate (KTF) in bulk drug and in tablets using cerium(IV) as the oxidimetric agent. In titrimetry (method A), the drug was treated with a measured excess of cerium(IV) in H2SO4 medium and after a standing time of 10 min, the surplus oxidant was determined by back titration with iron(II). The spectrophotometric procedures involve addition of a known excess of cerium(IV) to KTF in acid medium followed by the determination of unreacted oxidant by reacting with either p-dimethyl amino benzaldehyde and measuring the resulting colour at 460 nm (method B) or o-dianisidine and subsequent measurement of the absorbance of coloured product at 470 nm (method C). Titrimetric assay is based on a 1 : 2 reaction stoichiometry between KTF and cerium(IV) and the method is applicable over 2-18 mg range. In spectrophotometry, regression analysis of Beer's law plots showed a good correlation in 0.4-8.0 and 0.4-10.0 g mL(-1) KTF ranges for method B and method C, respectively, and the corresponding molar absorptivity coefficients are calculated to be 4.0 × 10(4) and 3.7 × 10(4) L mol(-1) cm(-1).