👨‍💻 Quantitation of MNP & CPNP in Rifampin and Rifapentine by LC-MS/MS

Since the discovery of potentially mutagenic nitrosamine impurities in pharmaceuticals in 2018, liquid chromatography-mass spectrometry (LC-MS) methods have been widely applied for the trace level quantification of nitrosamines. As more nitrosamines and drug samples are analyzed, method accuracy is increasingly recognized as a major analytical challenge. Matrix effects can have a significant adverse impact on method accuracy but have not attracted much attention in nitrosamine quantification literature. In this study, we observed severe matrix effects when adapting LC-MS method conditions from a published and validated method for the analysis of nitrosamines in tuberculosis drugs. Several approaches were explored to mitigate these matrix effects, including using stable isotope-labeled internal standards, modifying LC conditions and sample concentration, and quantifying with standard addition instead of an external calibration method. The results underscore the importance of monitoring matrix effects and validating nitrosamine quantification procedures for specific sample matrices. Finally, two LC-MS/MS methods are presented with validation data for the quantification of 1-methyl-4-nitrosopiperazine (MNP) in rifampin and 1-cyclopentyl-4-nitrosopiperazine (CPNP) in rifapentine and revealed high nitrosamine levels in the tested samples that far exceeded recommended acceptable intake limits.

Open Access: https://www.sciencedirect.com/science/article/pii/S2949771X24000033


This application note was developed to provide an analytical resource for regulators and industry to monitor nitrosamine impurities in drug products, drug substances or other matrices. It is intended to serve as a resource for informational purposes only and not as an USP-NF compendial documentary standard. This document was developed by USP staff without a public comment period and does not reflect USP or USP’s Expert Body opinions on future revisions to official text of the USP-NF. Parties relying on the information in this document bear independent responsibility for awareness of, and compliance with, any applicable federal, state, or local laws and requirements.