Ultra-Trace Quantification of N-Nitroso-desmethyl-sumatriptan with Interference Resolution Using LC–TQ

Significance of the topic

N-nitroso-desmethyl-sumatriptan is a drug substance-related nitrosamine impurity (NDSRI) formed from sumatriptan succinate and classified as a Category 1 genotoxic impurity. Regulatory limits for such nitrosamines are extremely low (specified here at 0.0428 ppm relative to the API), so analytical methods must deliver high sensitivity, selectivity and reproducibility. Robust trace-level quantification is essential for release testing, stability studies and regulatory compliance in pharmaceutical quality control.

Objectives and study overview

The poster describes development and validation-like evaluation of an LC–TQ method for ultra-trace quantification of N-nitroso-desmethyl-sumatriptan in sumatriptan succinate. Key goals were to separate the API from the nitrosamine, achieve sensitivity well below the specification, demonstrate linearity and repeatability, and assess recovery in spiked API samples. The work used an Agilent LC/TQ platform to target an LOD at least 20-fold lower than the regulatory specification and to establish reliable LOQ and method performance metrics.

Used instrumentation

• UHPLC: Agilent 1290 Infinity III.
• Triple quadrupole MS: Agilent 6495D LC/TQ, operated in positive ESI-AJS mode.
• Column: Poroshell 120 EC-C18, 3.0 × 150 mm, 2.7 µm, column temperature 40 °C.
• Autosampler: 15 µL injection volume, 8 °C tray.
• MS and source conditions: capillary 3500 V, nozzle 500 V, drying gas 17 L/min at 250 °C, sheath gas 12 L/min at 350 °C, nebulizer 55 psi.
• Detection modes: MRM (positive) for nitrosamine, UV detection at 228 nm for API.
• Mobile phases: A = 2 mM ammonium formate + 0.1% formic acid in water; B = 0.1% formic acid in 9:1 acetonitrile:water.
• Flow: 0.4 mL/min, with a gradient program spanning 90:10 to 10:90 (A:B) across 14 minutes and flow to MS enabled between 8 and 12 min using a diverter valve.
• MRM transitions for N-nitroso-desmethyl-sumatriptan: precursor m/z 311.1; product ions m/z 143, 186.1 and 216.1 with optimized collision energies (CE 33, 20 and 6 respectively).

Methodology

Samples and standards were prepared in methanol:water (1:1, v/v). A calibration series was established covering the low-ppb range (reported range 0.00214 to 0.1 ppm relative to API). Method performance was evaluated on a representative API sample prepared at 10 mg/mL and on samples spiked at LOQ and at the regulatory specification level, with replicate injections to assess linearity, recovery, repeatability (RSD) and limit of quantification.

Main results and discussion

• Chromatographic separation: Sumatriptan API eluted at ≈2.3 min, while the NDSRI eluted at ≈8.8 min, giving clear baseline separation and allowing selective MS detection of the nitrosamine while UV monitored the API.
• Linearity: Calibration over 0.00214–0.1 ppm produced excellent linearity with r2 = 0.9998, demonstrating quantitation capability across more than an order of magnitude around the specification.
• Sensitivity: The study targeted an LOD at least 20× lower than the spec limit; the calibration range and lowest calibrated level (0.00214 ppm) indicate the method reaches sub-specification concentration levels suitable for ultra-trace work.
• Repeatability and precision: For standard and spiked samples at specification-level concentrations the reported RSD values were low (example values: 1.3% for standard, 2.01% for spiked standard). At the LOQ-level injections RSDs as low as 0.64% (standard) and 1.3% (spiked) were reported. A single area RSD example of 4.67% was noted for a 0.048 ppm injection in a specific test.
• Recovery and sample content: Replicate API samples (10 mg/mL) contained NDSRI below the LOQ. Recovery for spiked samples was approximately 95% at both LOQ and specification levels (reported 95.5% at LOQ and 95.2% at specification), indicating good method accuracy in the API matrix.
• Interference resolution: The combination of chromatographic separation and MRM transitions provided selective detection of the nitrosamine in the presence of the API and other matrix components, enabling reliable low-ppb quantitation.

Benefits and practical applications

• Regulatory compliance: The method supports monitoring of a genotoxic nitrosamine impurity at levels below regulatory specifications, suitable for release testing and stability evaluation.
• High sensitivity and selectivity: MRM on a triple quadrupole with adequate chromatographic separation reduces false positives from co-eluting matrix components and enables trace-level reporting.
• Routine QC adoption: The workflow (simple sample preparation in MeOH:H2O) and robust instrument platform make the method amenable to routine use in quality-control laboratories.
• Batch testing and process monitoring: The approach can be used for batch release testing, spike/recovery verification and raw-material surveillance where nitrosamine formation risk exists.

Future trends and potential applications

• Broader nitrosamine panels: Expansion to simultaneous screening and quantification of multiple NDSRIs using scheduled MRM or multi-analyte methods to increase throughput.
• High-resolution MS complement: Use of HRMS for structural confirmation and untargeted screening of unexpected nitrosamines or related impurities.
• Automation and sample preparation: Automated dilution and SPE workflows to increase throughput and lower variability for routine QC labs.
• Isotopically labeled internal standards: Adoption of stable-isotope standards for each nitrosamine to improve accuracy and compensate for matrix effects.
• Regulatory tightening and harmonization: Anticipate more stringent limits and recommended analytical practices, driving further sensitivity and method validation rigor.

Conclusions

The presented LC–TQ method on Agilent 1290/6495 hardware demonstrates robust and sensitive quantification of N-nitroso-desmethyl-sumatriptan in sumatriptan succinate. Key outcomes include clear chromatographic separation of API and NDSRI, excellent linearity (r2 = 0.9998) across the low-ppb range, consistent recoveries (~95%) in spiked API samples and repeatability with RSDs well below typical QC thresholds. The method is suitable for routine monitoring of this genotoxic impurity, though reporting in the source material shows inconsistent phrasing about the LOQ relative to the specification and would benefit from explicit numerical statements of LOQ and LOD in final validation documentation.

Reference

1. U.S. Food and Drug Administration. Guidance on acceptable intake limits for nitrosamine impurities (CDER). (FDA guidance document cited in source).
2. Agilent Technologies. Application note: Analysis of nitrosamine impurities using the 6495 triple quadrupole LC/MS system. (Agilent application note cited in source).