First derivative spectrophotometric and LC determination of benoxinate hydrochloride and its degradation products

Two methods are presented for the determination of benoxinate HCl and its a cid and alkali-induced degradation products using first derivative (D-1) sp ectrophotometry with zero-crossing measurements and liquid chromatography. Benoxinate HCl was determined by measurement of its first derivative amplit ude in mcllvaine's-citric acid phosphate buffer pH 7.0 at 268.4 and 272.4 n m in the presence of its alkali- and acid-induced degradation products, res pectively. The acid- and alkali-induced degradation products were determine d by measurement of their first derivative amplitude in the same solvent at 307.5 nm. The LC method depends upon using a mu bondapak CN column with a mobile phase consisting of acetonitrile-water-triethylamine (60:40:0.01, v/ v) and adjusted to apparent pH 7. Quantitation was achieved with UV detecti on at 310 nm based on peak area. The proposed methods were utilized to inve stigate the kinetics of the acidic and alkaline degradation processes at di fferent temperatures. The pH-rate profile of degradation of benoxinate HCl in Britton-Robinson buffer solutions was studied. (C) 2000 Elsevier Science B.V. All rights reserved.