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Sensitive and Selective Extraction-Free Spectrophotometric Assay of Chloroquine Phosphate in Pharmaceuticals Based on Ion-Pair Reaction with Bromocresol Green and Bromocresol Purple

Nagib Qarah AS, Basavaiah K and Swamy N

Chloroquine Phosphate (CQP) is an antimalarial agent extensively used in the treatment of malaria. Two spectrophotometric methods, which are rapid, simple, selective and sensitive, are presented for the determination of CQP in bulk and dosage forms using two sulphonphthalein dyes: Bromocresol Green (BCG method) and Bromocresol Purple (BCP method). The methods are based on the formation of chloroform-soluble ion-pairs, when CQP is reacted with either dye, suitable for measurement at 420 nm in both the methods. The effects of reaction time, dye concentration and reaction medium were carefully studied and optimized. Under the optimum reaction conditions, Beer's law is obeyed overconcentration ranges 1-20 and 0.5-12 μg mL-1 CQP (base) for BCG method and BCP method respectively, with corresponding molar absorptivity values of 1.79 × 104 and 3.09 × 104 L mol-1 cm-1. The calculated limits of detection (LOD) and quantification (LOQ) are 0.27 and 0.82 μg mL-1 (BCG method); 0.15 and 0.46 μg mL-1 (BCP method). Intra-day and inter-day %RSD values were ≤1.56% and ≤1.83% whereas the respective %RE values were better than 2%. Robustness of the methods was determined by performing analysis with slightly altered optimum conditions while ruggedness was tested by inter-personnel as well as inter-equipment variations; the %RSD values were within the accepted limits in both instances. Method selectivity was as ascertained by placebo blank and synthetic mixture analysis with no detectable interference from co-formulated substances in the assays. The methods were applied to the determination of CQP in tablets, suspension and injections with satisfactory results. Accuracy was also confirmed by recovery test via standard-addition procedure.