Related substances Determined by HPLC (General requirements 0512). Test away from light. Prepare this reagent freshly before using.
Solvent: Acetonitrile-water (15:85)
Test solution: Take appropriate amount of this product, accurately weighed, dissolve in solvent and quantitatively dilute to make a solution containing about 1mg per 1ml.
Reference solution: Take theophylline RS about 10mg, accurately weighed, put it in a 10ml volumetric flask, dissolve it in solvent and dilute it to the mark line, shake it up, accurately measure 1ml reference solution and 1ml test solution, place it in the one same 100ml volumetric flask, dilute to the mark line with solvent, shake up, accurately measure 5 ml, place in a 50 ml volumetric flask, dilute to the mark line with solvent, and shake up.
Chromatographic conditions: Use ostade-cylsilane as stationary phase, use acetonitrile- phosphate buffer (pH 5.8) (15:85) as mobile phase; detection wavelength is 273nm, injection volume is 10μl.
Requirements of System Suitability: In the chromatogram of reference solution, the Resolution (R) between theophylline and doxofylline should be greater than 10. The Number of Theoretical Plates (n) should not be less than 2000 based on the peak of doxofylline.
Method of assay: The test solution and the reference solution are accurately weighed and injected into the liquid chromatograph, and the chromatogram was recorded to three times the retention time of the main component peak.
Limit: If there is a chromatographic peak in the chromatogram of the test solution that is consistent with the retention time of theophylline, the peak area shall not exceed 0.1% according to the external standard method; the other individual impurity peak area shall not be larger than the doxofylline peak area in the reference solution ( 0.1%); the sum of the peak areas of other impurities shall not be greater than four times (0.4%) of the area of the doxofylline peak in the reference solution.