Sensitive and selective extraction free spectrophotometric assay of diethylcarbamazine citrate in bulk drugand in formulations using two sulfonphthalein dyes

Diethylcarbamazine citrate (DEC) is an anthelmintic used in the treatment of filarial infections. Two rapid, simple, sensitive and selective spectrophotometric methods are presented for the determination of DEC in pharmaceuticals. The methods are based on the formation of chloroform soluble 1:1 ion pair complexes (DEC base:dye) formed between DEC base and sulphonphthalein dyes, bromophenol blue BPB, (method A) and bromothymol blue BTB, (method B). The complexes formed were measured directly (without extraction) at 430 nm (method A) and 440 nm (method B). The experimental conditions were optimized and the systems obey Beer’s law for 0.2-9.0 and 0.4–14.0 ?g mL-1 DEC base for method A and method B respectively. The molar absorptivity and Sandell sensitivity were calculated to be 4.985×104 L mol -1 cm-1 and 0.0079 ng cm-2 ; 3.152×103 L mol -1 cm-1 and 0.0124 ng cm-2 using BPB and BTB, respectively. The limits of detection and quantification were calculated to be 0.12 and 0.35; 0.08 and 0.24 ?g mL-1 using BPB and BTB respectively. The relative standard values for intra- day and inter- day precision were less than 3 %, and the accuracy was better than 3 % for both methods. The methods were successfully applied to the determination of DEC base in formulations with mean percentage assay values in the 98.6 to 102.5 range with standard deviation being less than 2%. The accuracy of the methods was further ascertained by parallel determination using the official method and by recovery studies.