Colorimetric assay of propranolol tablets by derivatization: novel application of diazotized 4-amino-3,5-dinitrobenzoic acid (ADBA).

A novel colorimetric assay of propranolol tablets has been developed. The assay is based on chemical derivatization (aromatic ring derivatization technique) using diazotized 4-amino-3,5-dinitrobenzoic acid (ADBA) as the chromogenic derivatizing reagent and resultant formation of azo dyes. Optimization studies established an optimal reaction time of 5 min at 30 degrees C after mixing on a Vortex mixer the drug/reagent mixture for 10 s. A new absorption maximum (lambda(max)) was found at 470 nm, which was selected as the analytical wavelength. The assays were linear over 1-8 microg/mL propranolol, and the reaction occurred by a 1:1 reagent/drug stoichiometric ratio. The developed method has a low limit of detection of 0.76 microg/mL and is reproducible. It has been applied successfully to the assay of propranolol tablets and is of equivalent accuracy (p > 0.05) with the official (British Pharmacopoeia) ultraviolet spectrophotometric method. The new method has the main advantage of using more affordable instrumentation and could be applied to the in-process quality control of propranolol tablets.