Development and validation of HPLC method for determination of clotrimazole and its two degradation products in spray formulation.

A novel simple isocratic HPLC method with UV detection for the determination of three compounds in spray solution (active component clotrimazole and two degradation products imidazole and (2-chlorophenyl)diphenylmethanol) using ibuprofen as an internal standard was developed and validated. The complications with different acido-basic properties of the analysed compounds in HPLC separation - while clotrimazole has pK(a) 4.7, imidazole has pK(a) 6.9 compared to relatively more acidic (2-chlorophenyl)diphenylmethanol - were finally overcome using a 3.5mum Zorbax((R)) SB-Phenyl column (75mmx4.6mm i.d., Agilent Technologies). The optimal mobile phase for separation of clotrimazole, degradation products imidazole and (2-chlorophenyl)diphenylmethanol and ibuprofen as internal standard consists of a mixture of acetonitrile and water (65:35, v/v) with pH* conditioned by phosphoric acid to 3.5. At a flow rate of 0.5mlmin(-1) and detection at 210nm, the total time of analysis was less than 6min. The method was applied for routine analysis (batch analysis and stability tests) in commercial spray solution.