A new HPLC-DAD method for the concurrent determination of hydroquinone, hydrocortisone acetate and tretinoin in different pharmaceuticals for melasma treatment

A new simple and robust HPLC-DAD method was developed for the concurrent analysis of hydroquinone (HQ), hydrocortisone acetate (HCA) and tretinoin (TRN) triple combination for the first time using an Inertsil ODS 3-C18 column (150 mm × 4.6 mm, 5 μm particle size) column with 0.05 M phosphate buffer (pH 5.0) and acetonitrile at a ratio of (10:90, v/v) as a mobile phase, eluted by an isocratic elution mode at a flow rate of 1.0 mL/min and detected at 265 nm. Mefenamic acid was used as an internal standard (I.S.). The method produced linear responses in the concentration range of 10-200, 5-100 and 1-40 μg/mL, with detection limits of 2.01, 1.13 and 0.28 × 10^-3 and quantitation limits of 6.11, 3.41 and 0.87 × 10^-3 μg/mL for HQ, HCA and TRN, respectively, and a correlation coefficient higher than 0.9998. All validation requirements were satisfied by proving its linearity, precision, accuracy, robustness and specificity. The method was extended for application in triple combination cream, HQ/TRN co-formulated cream and HQ and TRN single ingredient cream with a recovery >97%.