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 pKa 4.7, imidazole has pKa 6.9 compared to relatively more acidic (2-chlorophenyl)diphenylmethanol – were finally overcome using a 3.5 μm Zorbax® SB-Phenyl column (75 mm × 4.6 mm 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 0.5 ml min−1 and detection at 210 nm, the total time of analysis was less than 6 min.The method was applied for routine analysis (batch analysis and stability tests) in commercial spray solution.