A new RP-HPLC method for the simultaneous detection and quantification of minocycline and ascorbic acid in pure forms and combined pharmaceutical dosage forms

We report the first reverse-phase, high performance liquid chromatography (RP-HPLC) method for the rapid and simple simultaneous detection and quantification of minocycline and ascorbic acid in raw and pharmaceutical dosage forms. Detection was performed on a Sunniest C-18 column (5 μm particle size, 150 mm × 4.6 m mi.d(, at UV wavelength of 255 nm. The mobile phase consisted of potassium dihydrogen phosphate pH 2.8: Acetonitrile: Methanol (85:10:5), with 0.6 v/v% TEA and adjusted with orthophosphoric acid to a pH of 2.8 in an isocratic elution mode, with a flow rate of 0.8 mL/min. Performed analysis on the method proved that the newly developed method was sensitive, selective, accurate, precise, and robust. The method demonstrated good linearity with r2 = 0.9999 (n = 7) for both drugs and was validated in the sample concentration ranges of 1–100 and 5–500 µg mL−1 for minocycline and ascorbic acid, respectively. Both intra- and inter-day precisions were less than 2 % for both drugs, with limits of detection of 1.59 and 7.89 µg/mL and limits of quantification of 4.83 and 23.89 µg/mL, for minocycline and ascorbic acid, respectively. The applicability of the method was demonstrated by accurately determining the drug content of two commercial pharmaceutical formulations.