New colorimetric methods for the determination of indapamide and its formulations

Two simple and sensitive methods for the determination of indapamide in pure and in dosage forms are developed. These methods are based on the oxidation of indapamide with iron(II) in acidic medium. The liberated iron(II) reacts with 1,10-phenanthroline (Method A) and the ferroin complex is colorimetrically measured at lambda (max) 509 nm against reagent blank. Method B is based on the reduction of Fe(III) by the drug. Iron(II) forms a colored complex (lambda (max) 522 nm) with 2,2'-bipyridyl. Optimization of the experimental conditions is described. Beer's law is obeyed in the concentration range 1.0-12 mug ml(-1) and 4.0-18 mug ml(-1) for A and B, respectively. The apparent molar absorptivity and Sandell sensitivity for method A is 3 x 10(4) L mol(-1) cm(-1) and 0.0188 mug cm(-2), while for method B is 2.3 x 10(4) L mol(-1) cm(-1) and 0.0159 mug cm(-2). The detection and quantification limits are calculated. The developed methods are applied successfully for the determination of indapamide in pure and in tablet form without interference from common excepients.