Cationic Impurities in Colesevelam Analyzed by MPIC Using IonPac NS2

Significance of the Topic

Cationic surfactants such as cetylpyridinium are widely used in pharmaceutical formulations, including colesevelam mouthwash, to sequester bile acids and provide therapeutic benefits. Accurate detection and quantification of trace impurities arising from manufacturing or degradation are critical to ensure product safety, efficacy, and regulatory compliance.

Objectives and Overview of the Study

This study aims to develop and validate a robust analytical method based on mobile-phase ion chromatography (MPIC) with suppressed conductivity detection for the separation and quantification of cetylpyridinium and related cationic impurities in colesevelam mouthwash formulations.

Methodology and Instrumentation

Key components of the method include:

• Chromatographic system: Thermo Scientific™ Dionex™ ICS-3000 or ICS-5000 ion chromatography
• Column: Acclaim™ Surfactant Plus IonPac® NS2, 3.0 × 150 mm, 5 µm
• Mobile phase: gradient of acetonitrile, water, formic acid, and heptafluorobutyric acid (ion-pairing agent)
• Flow rate: 0.5 mL/min; injection volume: 5–10 µL; column temperature: 25 °C
• Detection: suppressed conductivity with Dionex™ CSRS™ 300 suppressor; optional UV monitoring at 220 nm

Main Results and Discussion

The optimized method achieved baseline separation of seven cationic impurities (6-aminohexyltrimethylammonium, 6-bromohexyltrimethylammonium, decylamine, aminodi(hexyltrimethylammonium), decyl-6-aminohexyltrimethylammonium, didecylamine, and cetylpyridinium). Performance metrics included:

• Resolution >1.5 between adjacent peaks
• Limits of quantification: 0.1–0.7 µg/mL
• Linear range up to 25 µg/mL with correlation coefficients (r2) >0.999
• Reproducible retention times (<1% RSD) and peak areas (<2% RSD)

Suppressed conductivity detection offered high sensitivity and minimal matrix interferences, enabling reliable impurity profiling.

Benefits and Practical Applications

This MPIC method provides:

• High selectivity for charged surfactant impurities in complex pharmaceutical matrices
• Rapid analysis suitable for routine quality control laboratories
• Trace-level quantification to meet stringent regulatory requirements
• Compatibility with existing IC systems and optional coupling to charged-aerosol detectors

Future Trends and Possibilities

Emerging directions include:

• Automated sample preparation and injection for higher throughput
• Use of greener mobile phases to reduce organic solvent consumption
• Extension to other ionic surfactants and quaternary ammonium compounds
• Integration with mass spectrometry for structural elucidation of unknown impurities

Conclusion

The validated MPIC method employing suppressed conductivity detection and an Acclaim Surfactant Plus column offers a sensitive, selective, and robust approach for monitoring cetylpyridinium and related cationic impurities in colesevelam mouthwash. This technique supports reliable quality control and ensures product safety.

Reference

Thermo Fisher Scientific application notes and technical bulletins (2012–2013)