Spectrophotometric microdetermination of some pharmaceutically important aminoquinoline antimalarials, as ion-pair complexes

A simple, rapid, accurate and sensitive spectrophotometric method for the microdetermination of some pharmaceutically important aminoquinoline antimalarials, namely amodiaquine dihydrochloride (I), chloroquine phosphate (II) and primaquine phosphate (III) is described. The method is based on the interaction of these drugs with calmagite indicator to give highly coloured ion-pair complexes which exhibit maximum absorption at 663, 665 and 666 nm, respectively, Beer's law is obeyed in the concentration ranges 1.0-25.0, 1.0-28.0 and 1.0-33.0 mu g/ml for the drugs I, II and III, respectively. For more accurate analysis, the Ringbom optimum concentration ranges are 2.5-22.5, 2.0-26.0 and 3.0-30.0 mu g/ml, respectively. The apparent molar absorptivities were calculated. Statistical treatment of the experimental results indicates that the method is sufficiently accurate and precise. The accuracy of the method is indicated by the recovery (99.8 +/- 1.4%) and the precision by the relative standard deviation (<1.5%). The proposed method has been applied to the determination of these drugs in certain formulations, with results that compared favourably with those obtained by the official methods.