Derivatization of genotoxic nitroaromatic impurities for trace analysis by LC-MS

Trace level analysis of genotoxic impurities requires highly sensitive analytical methodologies and poses a tremendous challenge for the pharmaceutical industry. Nitroaromatic compounds, among the genotoxic structural alerts, are widely used as starting materials or intermediates for the synthesis of active pharmaceutical ingredients (APIs). If their genotoxicities are confirmed, the nitroaromatic impurities need to be controlled under the Threshold of Toxicological Concern (TTC) level. In general, HPLC-UV methodology is not suitable due to the inadequate sensitivity of the UV detection. Many nitroaromatic compounds used in the pharmaceutical industry are non-volatile, and thus the application of GC is limited. If used directly, LC-MS methodology is less useful to neutral nitroaromatic compounds that lack ionization efficiency. In this article, the authors report a new methodology to detect and quantify trace nitroaromatic compounds by LC-MS after chemical derivatization, where the nitroaromatic compounds are reduced to the corresponding ionizable aromatic amines. It is the authors' hope to provide a general methodology for detecting and quantifying nitroaromatics at trace levels. The reported method is validated for sensitivity, linearity, precision and accuracy. This methodology has been successfully applied to one of Celgene's projects and the detailed case study is provided in this article.