HPLC methods for measuring benzocaine and its degradation products in Herplex gel

Abstract

Benzocaine as a main active substance in the Herplex gel, Galex d.d. used for healing of fever blister is treated as a local anaesthetic. According to European Pharmacopoeia titration method for determination of benzocaine is applied in the pharmaceutical industry. However its degradation products (determination of p-nitrobenzoic acid ethylester (EPNB) and p- aminobenzoic acid (PABA)) are not described in pharmacopoeias (neither Ph. Eur nor USP). Two high performance liquid chromatography methods with UV detection were developed for determination of benzocaine and both degradation products (p-nitrobenzoic acid ethylester and p-aminobenzoic acid). Procedures for extraction of these active from the Herplex gel were developed too. Optimum results were obtained with a column Eclipse XDB - C 18 (4.6 x 150 mm, 5 µm) and a mobile phase comprising glacial acetic acid solution (10%, v/v) and methanol. Injection volume was set to 10 µml and temperature to 40 ˚C. Other conditions used in methods varied. The first method for benzocaine and EPNB was set to flow rate 2 ml/min, detection time 30 min and mobile phase was carried as a gradient profile programme whereas the second method for PABA was set to flow rate 1 ml/min, detection time 10 min and glacial acetic acid solution and methanol in the rate of 90 :...