Spectrophotometric determination of dothiepin hydrochloride in pharmaceuticals through ion-pair complexation reaction

Abstract

Two simple, sensitive and extraction-free spectrophotometric methods are described for the determination of dothiepin hydrochloride (DOTH) in both pure form and in pharmaceutical tablets. The methods are based on ion-pair complex formation between dothiepin base (DOT) and two acidic dyes, namely, bromophenol blue (BPB) or bromocresol green (BCG) with absorption maximum at 425 nm for BPB method or 430 nm for BCG method. Beer's law is obeyed over the concentration ranges of 1.0-15.0 and 1.0-17.5 μg mL-1 DOT for BPB and BCG methods, respectively. The molar absorptivity values and Sandell's sensitivity values are reported for both methods. The limits of detection (LOD) and quantification (LOQ) were calculated to be 0.18 and 0.53 μg mL-1 for BPB method, and 0.17 and 0.50 μg mL-1 for BCG method, respectively. The stoichiometry of the complex in either case was found to be 1:1 and the conditional stability constant (KF) of the complexes has also been calculated. The proposed methods were applied successfully to the determination of DOTH in pure form and in its tablet form with good accuracy and precision. Statistical comparison of the results was performed using Student's t-test and variance ratio F-test at 95% confidence level and there was no significant difference between the official and proposed methods with regard to accuracy and precision. Further, the validity of the proposed methods was confirmed by recovery studies via standard addition technique.