The application of LC–NMR and LC–MS for the separation and rapid structure elucidation of an unknown impurity in 5-aminosalicylic acid

This work has demonstrated the usefulness of combining liquid chromatography–nuclear magnetic resonance spectroscopy (LC–NMR) and liquid chromatography–mass spectrometry (LC–MS) methodologies for a rapid identification of an unknown impurity (N1) in the drug 5-aminosalycilic acid. Complementary information obtained from the two methods has revealed plenty of structural information and led to the fast on-line structure determination of N1 prior to its isolation and purification. The analysis of LC–NMR and LC–MS spectra revealed that N1 and 5-aminosalycilic acid are structurally closely related compounds. The structure of N1 was later confirmed by high-resolution NMR spectroscopy of the isolated compound and the atom assignment was made. The approach described here has potential for 5-aminosalycilic acid impurity profiling and monitoring the production process.