Structural Identification and Analysis of Degradation Impurities in Nimodipine Oral Solution

OBJECTIVE To identify and analyze two unknown degradation impurities in nimodipine oral solution. METHODS The chemical structure of the unknown impurity was deduced by two-dimensional liquid chromatography-high resolution mass spectrometry(2DLC-HRMS), and the impurity monomer was obtained by directional synthesis. The structure of the impurity was confirmed by ¹H-NMR and ¹³C-NMR, chromatographic separations were performed on an Thermo Syncronis C₁₈(250 mm×4.6 mm, 5 μm) column. Using 5 mmol·L^-1 potassium dihydrogen phosphate buffer(pH 2.8) as mobile phase A, while methanol-acetonitrile(50:50) was mobile phase B, with gradient elution. The mobile phase was pumped at 1.0 mL·min^-1. The column temperature was 30℃. The detection wavelength was 235 nm. RESULTS Nimodipine and its related substances had good separation. The correction factors of every impurities ranged from 0.8 to 1.1. CONCLUSION The established method has good specificity and can effectively isolate and determine the related substances in nimodipine oral solution. This study provides a reference to guide the impurity control of nimodipine oral solution and other dosage forms.