APPS: Method for the Analysis and Quantitation of Pharmaceutical Counterions Utilizing Hydrophilic Interaction Liquid Chromatography

Importance of the Topic

Pharmaceutical salts are used to enhance physiochemical properties and bioavailability of drug molecules. More than half of marketed drugs exist as salt forms so reliable analysis of active ingredients and their counterions is critical for quality control in pharmaceutical development and manufacturing.

Objectives and Study Overview

This work aimed to create a single hydrophilic interaction liquid chromatography method able to separate and quantify both cationic and anionic counterions alongside active pharmaceutical ingredients in drug salt formulations. The method addresses the need to streamline routine quality control by combining multiple analyses into one robust protocol.

Methodology and Instrumentation

The approach employs a zwitterionic HILIC stationary phase with gradient elution and evaporative light scattering detection to achieve simultaneous visibility of seven common counterions and active ingredients. Dynamic calibration and reproducibility studies establish method performance.

Instrumentation

• ACQUITY Arc Premier LC System with Atlantis Premier BEH Z-HILIC column 4.6×100 mm 2.5 μm at 40 °C
• Gradient from 80 to 10 percent acetonitrile in water over ten minutes with constant 5 percent ammonium formate and formic acid additives
• Waters 2424 ELSD at 40 psi gas pressure, drift tube 50 °C, nebulizer off, detector gain 75

Key Results and Discussion

Seven ions including nitrate, phosphate, chloride, sodium, potassium, magnesium and calcium were resolved with area and retention time RSDs below 5 and 6 percent over ten injections. Calibration curves for sodium, chloride and potassium showed linearity coefficients above 0.997, enabling accurate quantitation over a dynamic range. Application to naproxen sodium, metformin hydrochloride and losartan potassium formulations yielded counterion concentrations consistent with expected values while simultaneously observing API retention.

Benefits and Practical Applications

The unified HILIC-ELSD protocol reduces analysis time and resource consumption by replacing separate assays for anions and cations. It supports comprehensive quality control of diverse pharmaceutical salt forms and adapts to combination drug products.

Future Trends and Potential Applications

Integration with mass spectrometry promises enhanced specificity and broader detection of salt forms. Advances in stationary phases and detector sensitivity will further improve throughput and enable automated high-throughput screening in pharmaceutical development.

Conclusion

A robust HILIC-ELSD method has been developed for simultaneous identification and quantification of pharmaceutical counterions and active ingredients in drug salts. Its precision, linearity and reproducibility make it a valuable tool for quality control in pharmaceutical research and manufacturing.

References

• Saal C Becker A Pharmaceutical salts A summary on doses of salt formers from the Orange Book European Journal of Pharmaceutical Sciences 2013 49 4 614 623
• Staiger B What are salt forms of drugs and why are they different Walrus Health 2018
• Savjani KT Gajjar AK Savjani JK Drug Solubility Importance and Enhancement Techniques International Scholarly Research Notices Pharmaceutics 2012 2012 1 10
• Dotzel M Q6A Specifications Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products US Food and Drug Administration 2000
• Walter T Berthelette K Patel A Alden B McLaughlin J Field J Lawrence N Shiner S Introducing Atlantis BEH Z HILIC A Zwitterionic Stationary Phase Based on Hybrid Organic Inorganic Particles Waters Corporation Application Note 2021
• Waters Corporation Evaporative Light Scattering Detector Operators Guide 71500121802 Revision B 2006