Sensitive spectrophotometric determination of benoxinate hydrochloride using different aldehydes through condensation reactions

Simple and sensitive spectrophotometric methods have been developed for the quantitative determination of benoxinate HCl in bulk and in pharmaceutical formulations. The first method depends on condensation of primary aromatic amine group of benoxinate HCl with 4-dimethylaminobenzaldehyde (PDAB) in presence of glacial acetic acid and the orange red colour developed was measured at 453 nm. The linearity range was found to be 20–120 μg ml−1. The second is based on the reaction with 4-dimethylaminocinnamaldehyde (DMAC) in 50% sulphuric acid producing a coloured product which absorbs maximally at 549 nm. Beer’s law is obeyed in the concentration range 5–50 μg ml−1 of benoxinate HCl. The third method is based on the reaction of benoxinate HCl with acetylacetone and formaldehyde in presence of acetate buffer pH 5.8 (Hantzsch reaction) and the colour developed was measured at 358 nm. The absorbance is proportional to benoxinate HCl concentration in the range 2–20 μg ml−1. The optimum experimental parameters for the reactions have been studied. The validity of the described procedures was assessed. Statistical analysis of the results has been carried out revealing high accuracy and good precision. The suggested procedures could be used for the determination of benoxinate HCl in ophthalmic solution. The procedures were rapid, simple and suitable for quality control application.