Colorimetric Assay Of Naproxen Tablets by Derivatization Using 4-Carboxyl-2,6-Dinitrobenzene Diazonium Ion

A colorimetric assay of naproxen tablets based on chemical derivatization with the chromogenic reagent 4-carboxyl-2,6-dinitrobenzene diazonium ion was developed. The optimal reaction time was found to be 5 min at 30 o C after vortex mixing of the drug/reagent mixture for 10 s. The optimal analytical wavelength was found to be 470 nm and linearity of response was obtained between 1-7 μgml -1 of naproxen. The diazo coupling reaction occurred in a 2:1 reagent-drug stoichiometric ratio. The method is sensitive, accurate (mean recovery 101.06±3.06 %), reproducible (imprecision 3.03 % CV) and has a low limit of detection (0.95 μgm -1 ). It was applied in the assay of naproxen tablets with equivalent accuracy (p>0.05) to the official (BP) UV spectrophotometric method but combined the advantages of speed and more affordable instrumentation. The method can be applied in the in-process quality control of naproxen tablets. Keywords: Naproxen assay, 4-carboxyl-2,6-dintrobenzene diazonium ion (CDNBD), colorimetry, diazo coupling reaction East and Central African Journal of Pharmaceutical Sciences Vol. 12 (2009) 8-14