METHOD FOR THE ANALYSIS AND QUANTITATION OF PHARMACEUTICAL COUNTERIONS UTILIZING HYDROPHILIC INTERACTION LIQUID CHROMATOGRAPHY

Significance of the Topic

Pharmaceutical products often exist as salts to improve solubility and bioavailability. Accurate analysis of both active pharmaceutical ingredients (APIs) and their counterions is essential for quality control, regulatory compliance, and ensuring therapeutic efficacy. Traditional testing typically requires multiple chromatographic techniques, increasing time and cost. A unified hydrophilic interaction liquid chromatography (HILIC) method combined with evaporative light scattering detection (ELSD) addresses these challenges.

Objectives and Study Overview

This study aims to develop a single chromatographic approach for the separation and quantitation of common pharmaceutical counterions alongside their APIs. The method focuses on zwitterionic HILIC (Z-HILIC) to retain both cationic and anionic species and employs ELSD to detect non-chromophoric ions. Key performance metrics such as reproducibility, linearity, and applicability to drug formulations are evaluated.

Methodology

Separation was performed on an Atlantis BEH Z-HILIC column (4.6×100 mm, 2.5 μm) at 40 °C using a 10 min gradient of acetonitrile, water, 200 mM ammonium formate, and 2% formic acid. The flow rate was 1.4 mL/min with a 10 µL injection volume. Counterion standards were prepared at 0.1 mg/mL in 60% acetonitrile, and calibration solutions ranged from 1 to 100 mM. Method precision was assessed over ten replicate injections.

Applied Instrumentation

• UHPLC system: ACQUITY Arc Premier
• Column: Atlantis Premier BEH Z-HILIC 4.6×100 mm, 2.5 μm
• Detector: Waters 2424 ELSD (gas pressure 40 psi, drift tube 50 °C, detector gain 75, nebulizer off)

Main Results and Discussion

The method achieved high reproducibility with relative standard deviations below 6% for retention time and peak area across ten injections. Calibration curves for sodium, potassium, and chloride showed strong linearity (R2 > 0.997) on a log–log scale. Application to naproxen sodium, metformin hydrochloride, and losartan potassium formulations confirmed clear resolution of API and counterion peaks, enabling accurate quantitation in complex matrices.

Benefits and Practical Applications

This unified HILIC-ELSD method streamlines quality control by analyzing both ions and APIs in a single run, reducing analytical time and resource use. ELSD detection overcomes the lack of UV chromophores in many counterions, offering broad analyte coverage. The approach is well suited for R&D, routine QC, and regulatory testing of pharmaceutical salts.

Future Trends and Opportunities

Emerging HILIC stationary phases and enhanced detector technologies may further boost sensitivity and selectivity for trace counterions. Coupling with mass spectrometry could expand compound identification and confirmation. Automation and high-throughput platforms are anticipated to accelerate drug analysis workflows in pharmaceutical development and manufacturing.

Conclusion

A robust Z-HILIC-ELSD method has been established for simultaneous separation and quantitation of pharmaceutical counterions and APIs. The technique demonstrates excellent reproducibility, linearity, and applicability to real drug formulations, offering an efficient solution for comprehensive salt analysis in pharmaceutical quality control.

References

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