Quantitative Determination of Olanzapine in Tablets with Visible Spectrophotometry using Cerium(IV)sulphate and Based on Redox and Complexation Reactions

Abstract

Three sensitive spectrophotometric methods were developed and validated for the quantification of
olanzapine (OLP) in bulk drug and in tablets. The method involved treating OLP with a known excess
of cerium(IV) in acid medium followed by the determination of unreacted oxidant by three reaction
schemes in which cerium(IV) was reduced by an excess of iron(II), and the resulting iron(III) was
complexed with thiocyanate, tiron or ferrocyanide and absorbance measured at 480 nm (method A),
640 nm (method B) or 700 nm (method C). Absorbance decreased linearly with concentration over the
ranges 0.2-2.0 µg mL-1 (method A), 1.0-9.0 µg mL-1 (method B) and 0.3-3.0 µg mL-1 (method C). The
calculated molar absorptivity values were 10.94 x104
, 1.67 x104
and 4.52 x104
L mol-1 cm-1 for method
A, method B and method C, respectively; and the corresponding limits of quantification (LOQ) were
0.02, 0.11 and 0.03 µg mL-1. Precision results, expressed by the intra-day and inter-day relative
standard deviation values, were satisfactory, better than 3 %, and accuracy expressed as relative error
varied from 0.75 to 2.5 %. The methods were successfully applied to the determination of OLP in
tablets with mean percentage recoveries of 95.84 to 102.5% .The method validation results showed
that the sensitivity and selectivity of the methods were adequate for drug monitoring in industrial
quality control laboratories.