Determination of theophylline and acetaminophen in pharmaccutical co-crystals by HPLC

High-performance liquid chromatography (HPLC) is used to determine the theophylline and acetaminophen in pharmaccutical co-crystals. The optimal conditions are shown as follows: C18 column (250 mm × 4.6 mm, 5 μm, 120å), octadecyl bonded silica as stationary phase, 0.01 mol/L of potassium dihydrogen phosphate (pH 3.05) /methanol (80/20 of volumetric ratio) as mobile phase, 245 nm and 270 nm as detection wavelength, 1.0 mL/min of flow rate, 25℃ of column temperature and 20 μL of injection volume. The results show that the regression equations of acetaminophen and theophylline are y=0.651 1x + 6.610 4 and y=0.939 2x-5.575 1, respectively. Their corresponding R² are 0.994 5 and 0.998, respectively. Furthermore, there is a linear relationship within 5-500 μg/mL. This method provides the basis for investigating theophylline-acetaminophen binary system and affords the feasibility of their solubility domination.