Spectrophotometric Assay of Diethylcarbamazine Citrate in Pharmaceuticals and Human Urine via Ion-Pair Reaction Using Methyl Orange Dye

Two simple and moderately selective spectrophotometric methods are described for the determination of Diethylcarbamazine Citrate (DEC) in bulk drug, dosage forms and spiked human urine. The first method (method A) is based on the formation of yellow colored ion-pair complex between DEC and Methyl Orange (MO) dye, at pH 4.95 ± 0.05, which was extracted into chloroform and measured at 420 nm. The second method (method B) involved the breaking of yellow ion-pair complex in acid medium followed by the measurement of the free dye at 520 nm. Experimental parameters influencing the formation and extraction of the ion-pair complex in method A and breaking of the complex in method B were scrupulously examined and optimized. Beer’s law is obeyed over the concentration ranges of 10-90 and 5-100 μg mL-1 DEC with corresponding molar absorptivity values of 2.90×103 and 3.54×103 L mol-1 cm-1 for method A and method B, respectively. The Sandell’s sensitivity values were 0.1351 and 0.1106 μg cm-2 for method A and method B, respectively. The Limits of Detection (LOD) and Quantification (LOQ) were calculated to be 0.36 and 1.09 μg mL-1 (method A) and 0.34 and 1.02 μg mL-1 (method B). The composition of drug-dye ion-pair complex used in method A was found to be 1:1 by Job’s method of continuous variations. The proposed methods were validated for robustness, ruggedness and selectivity, and applied to the determination of DEC in tablet, syrup formulations and spiked human urine samples. The results demonstrated that the proposed methods are as accurate and precise as the reference method. The accuracy of the methods was further ascertained by recovery study via standard-addition method.