Nitrosamine impurities analysis solutions guide

Significance of the topic

Nitrosamines are small, often volatile, N-nitroso compounds classified as probable human carcinogens. Since multiple nitrosamine contaminations were reported in pharmaceuticals starting in 2018, regulatory agencies have required enhanced screening, identification, and control of both known small nitrosamines and Nitrosamine Drug Substance Related Impurities (NDSRIs). Accurate detection and quantitation are essential to protect patients, maintain drug efficacy, avoid costly recalls, and satisfy evolving global regulatory expectations. Measurement of precursors such as nitrite and amines is also critical because they inform nitrosation risk and mitigation strategies for APIs and excipients.

Objectives and overview

This application-focused guide presents analytical solutions spanning exploratory discovery to routine high-throughput monitoring of nitrosamine impurities. It aims to: 1) match analytical technologies to different stages of nitrosamine control (screening, confirmation, routine quantitation, precursor monitoring), 2) show how high-resolution accurate-mass (HRAM) and triple-quadrupole MS technologies complement each other, 3) describe ion chromatography (IC) approaches for nitrite/nitrate, and 4) illustrate automation and compliance-ready software for GMP workflows. The document collates validated methods, instrumentation choices, and practical performance targets relevant for pharmaceutical QA/QC and CDMOs.

Methodology and analytical approaches

The guide recommends a toolbox approach where method selection is driven by the analytical objective:

• Exploratory and absolute mass confirmation: LC-HRAM (Orbitrap Exploris 120) or GC-HRAM (Orbitrap Exploris GC) to provide high resolving power and mass accuracy for unambiguous identification and to eliminate false positives caused by close isotopic or isobaric interferences (example: NDMA vs DMF 15N isotope requiring ≥45,000 resolution and ~3 ppm mass accuracy).
• Routine targeted quantitation: LC-MS/MS with triple quadrupole instruments (TSQ Altis Plus, TSQ Quantis/Quantis Plus) for sensitive, high-throughput assays and low limits of quantitation suitable for batch release testing.
• Volatile nitrosamine panels: validated GC-HRAM methods for rapid separation of multiple nitrosamines (e.g., 15 compounds separated in <12 minutes) with LOQs substantially below typical regulatory limits.
• Precursor monitoring (nitrite/nitrate, free/secondary amines): Ion chromatography (Dionex ICS-6000 HPIC) with reagent-free KOH eluent and optional MS or conductivity/UV detection for selective quantitation of nitrite/nitrate at trace levels (reporting demonstrated from ~1 to 150 ppb).
• Integrated workflows and automation: Automated sample preparation (TriPlus RSH) to reduce contamination risk and improve reproducibility; solvent-exchange options for compatibility with LC- or GC-based final analysis.
• Combined targeted/untargeted strategy (SQUAD): single-injection approach that performs accurate quantitation of known targets while simultaneously acquiring data to discover unknown impurities.

Instrumentation used

• Orbitrap Exploris 120 Mass Spectrometer — LC-HRAM for accurate-mass confirmation and separation of near-isobaric species.
• Orbitrap Exploris GC Mass Spectrometer — GC-HRAM for sensitive analysis of volatile nitrosamines with high mass resolution.
• TSQ Altis Plus, TSQ Quantis Plus, TSQ Quantis — triple quadrupole MS systems for targeted LC- or GC-MS/MS quantitation.
• Vanquish Flex/Horizon/Core UHPLC and Acclaim 120 columns — high-performance LC separations for nitrosamines and related impurities.
• TraceGOLD TG‑1701MS GC columns — fast, robust GC separations for nitrosamine panels.
• Dionex ICS-6000 HPIC and IonPac AS19-4 µm column — IC solutions for nitrite/nitrate quantitation with reagent-free KOH eluent generation.
• TriPlus RSH — automated sample preparation and solvent exchange compatible with downstream LC- or GC-MS analysis.
• Chromeleon Chromatography Data System (CDS) — compliance-ready software for instrument control, data processing, audit trails, and reporting aligned with GMP requirements.

Main results and discussion

Key performance highlights presented in the guide include:

• GC-HRAM method validated for 15 nitrosamines in metformin: separation in under 12 minutes, LOQs <2 ppb (about 10× better than a 30 ppb regulatory threshold), and robust performance across multi‑day runs.
• LC-MS/MS methods for metformin: demonstrated LOQ of 5 ppb using APCI and 10 ppb using HESI with excellent reproducibility over >1,000 injections.
• IC-MS for nitrite/nitrate in microcrystalline cellulose: accurate, precise quantitation from ~1 to 150 ppb with little sample prep and same-run measurement of both anions.
• HRAM benefit: demonstrated ability to resolve NDMA from DMF isotopic interferences; HRAM acquisition markedly reduces false positives compared with unit-mass methods and can shorten chromatographic method development by relying on mass resolution to resolve close interferences.
• SQUAD approach: feasible single-injection workflow combining calibrated targeted quantitation with untargeted discovery, enabling efficient screening while preserving the ability to detect novel NDSRIs.

Discussion emphasizes that combining chromatographic selectivity with HRAM or triple-quadrupole sensitivity yields workflows that are fit-for-purpose for confirmation or routine release testing. Automation and compliance-ready software are highlighted as practical enablers that reduce contamination risk and regulatory burden.

Benefits and practical applications

• Regulatory compliance: methods and software support traceable, auditable workflows appropriate for GMP environments.
• Risk-based monitoring: IC nitrite/nitrate data support nitrosation risk assessments and excipient screening to prevent nitrosamine formation.
• Laboratory efficiency: triple quadrupole LC-MS/MS delivers high-throughput routine assays, while HRAM provides definitive confirmation of ambiguous findings.
• Robustness and throughput: validated methods demonstrate long-term stability (hundreds to thousands of injections) suitable for routine batch monitoring in QA/QC labs.
• Reduced false positives: HRAM minimizes misidentification from closely spaced isotopes or co-eluting matrix components, reducing unnecessary follow-up work and commercial impact.
• Automation: automated extraction and solvent exchange streamline sample handling, improving reproducibility and throughput while lowering contamination risk.

Future trends and potential applications

• Broader adoption of hybrid workflows combining HRAM for confirmation with triple‑quad for routine throughput; increasing use of SQUAD-style methods to balance discovery and quantitation in one analysis.
• Greater integration of IC-MS for routine precursor surveillance to inform preventive controls during API and formulation development.
• Expanded automation in sample preparation, including online sample cleanup and direct coupling to LC/GC to reduce manual steps and contamination sources.
• Development of curated nitrosamine/NDSRI spectral libraries, curation of retention time indices, and advanced informatics (including AI-assisted review) to accelerate unknown annotation and regulatory reporting.
• Ongoing method harmonization and cross‑laboratory validation as regulatory guidance evolves to include additional NDSRIs and tighter limits.

Conclusion

A multi‑tool analytical strategy—pairing sensitive triple‑quadrupole assays for routine monitoring, HRAM platforms for definitive identification, IC for precursor assessment, and automated sample preparation—provides pharmaceutical laboratories with robust, regulatory‑aligned capabilities to detect, quantify, and mitigate nitrosamine impurities. Compliance-ready software and validated workflows further support reproducible, auditable operations suitable for QA/QC and CDMO environments.

References

1. Thermo Fisher Scientific. HRAM LC‑MS method for the determination of nitrosamine impurities in drugs. Application note.
2. Thermo Fisher Scientific. Highly sensitive and robust LC‑MS/MS solution for quantitation of nitrosamine impurities in metformin drug products. Application note.
3. Thermo Fisher Scientific. GC Exploris HRAM validation of 15 nitrosamines in metformin drug substance. Application note.
4. Thermo Fisher Scientific. Determination of nitrite and nitrate from microcrystalline cellulose by ion chromatography. Application note.
5. Thermo Fisher Scientific. Automated sample preparation workflow for the analysis of nitrosamines in metformin using TriPlus RSH. Application note.
6. Thermo Fisher Scientific. Chromeleon Chromatography Data System (CDS) software brochure. Technical brochure.