New colorimetric methods for the determination of indapamide and its formulations

Two simple and sensitive methods for the determination of indapamide in pur e and in dosage forms are developed. These methods are based on the oxidati on of indapamide with iron(II) in acidic medium. The liberated iron(II) rea cts with 1,10-phenanthroline (Method A) and the ferroin complex is colorime trically 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 co mplex (lambda (max) 522 nm) with 2,2'-bipyridyl. Optimization of the experi mental conditions is described. Beer's law is obeyed in the concentration r ange 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 interfer ence from common excepients.