Rapid colorimetric assay of diclofenac sodium tablets using 4-carboxyl-2,6-dinitrobenzene diazonium ion (CDNBD)

This study describes a novel simple, rapid and sensitive colorimetric assay method for diclofenac sodium tablets. The method is based on a simple aromatic ring derivatization technique using newly developed 4-carboxyl-2, 6-dinitrobenzenediazonium ion (CDNBD) as chromogenic derivatizing reagent with subsequent formation of an azo dye. The diazo coupling reaction was carried out between CDNBD and diclofenac. Optimization studies for time and temperature was conducted using the method of steepest ascent. The UV absorption spectrum was recorded and the stoichiometric ratio for the drug and reagent was done by continuous variation method. Optimal calibration range was fixed (1-way ANOVA) and then the method was applied to dosage form analysis. Comparison of dosage form analysis was done with the BP HPLC method. The diazo coupling reaction is very fast and optimization studies established an optimal reaction immediately after mixing the reaction mixture in a vortex mixer for 10 sec. A new absorption maximum (lambdamax) at 470 nm was selected as analytical wavelength. The assays were linear over 1.35-10.8 microg/ml of diclofenac and the reaction required a 2:1 reagent/drug stoichiometric ratio. The new method has a low limit of detection of 0.27 microg/ml, and was reproducible over a three-day assessment of precision (RSD 2.31%). The method has been successfully applied to the assay of diclofenac sodium slow-release tablets and found to be of equivalent accuracy (p>0.05) with the official (B.P 1998) HPLC method. The new method has distinct advantages of speed, simplicity, sensitivity, and more affordable instrumentation and could find application as a rapid analytical method for diclofenac sodium tablets.