Simple and sensitive spectrophotometric determination of olanzapine in pharmaceutical formulations using two sulphonphthalein acid dyes

Two simple, sensitive and extraction-free spectrophotometric methods have been developed for the determination of olanzapine (OLP) both in pure form and in pharmaceutical formulations. The methods are based on the fort-nation of yellow coloured ion-pair complexes between OLP and two sulphonphthalein acid dyes, bromocresol purple (BCP) and bromothymol blue (BTB) with absorption maximum at 405 nm and 410 nm for BCP and BTB, respectively. The stoichiometry of the complex in either case was found to be 1: 1 and the conditional stability constant (K(F)) of the complexes has also been calculated. Reaction conditions were optimized to obtain the maximum colour intensity. Beer's law was obeyed in the concentration ranges of 1.0 - 10.0 and 1.0 - 8.0 mu g/mL with BCP and BTB, respectively. Various analytical parameters have been evaluated and the results have been validated by statistical data. The proposed methods have been applied successfully to the analysis of OLP in pure form and in its dosage forms and no interference was observed from common excipients present in pharmaceutical formulations