IICS: Improving the Quantitation of Unknown Trace Impurity Analysis of Active Pharmaceutical Ingredients Using HPLC with Charged Aerosol Detection

Importance of the Topic

Accurate mass balance and quantitation of trace impurities in active pharmaceutical ingredients (APIs) is essential to ensure drug safety, efficacy, and regulatory compliance. Uniform detector response simplifies quantitation when reference standards are unavailable.

Objectives and Study Overview

This work compares charged aerosol detection (CAD) to evaporative light scattering detection (ELSD) and UV detection for trace-impurity analysis. It introduces inverse gradient technology via a dual‐gradient HPLC system to minimize response variability during gradient elution.

Methodology and Instrumentation Used

Instrumentation:

• Dionex UltiMate 3000 HPLC with dual-gradient pump and Chromeleon CDS
• Corona ultra™ charged aerosol detector (CAD)
• Evaporative light scattering detector (ELSD) and diode array detector (UV/DAD)

Method:

• Analysis of phenolic model compounds and seven test APIs under isocratic and gradient conditions
• Implementation of postcolumn makeup solvent via a T-union to create an inverse gradient
• Comparison of limits of detection (LOD), calibration linearity, and response factor variability

Main Results and Discussion

CAD exhibited more consistent response factors across diverse analytes than ELSD and UV, reducing response RSD from ~60–73% (UV) and ~45% (CAD gradient) to ~13% with inverse gradient CAD. LOD for gallic acid improved from 31 ng (ELSD) to 4 ng (CAD). Inverse gradient negated solvent‐composition effects on nebulization efficiency, ensuring stable mass‐based detection.

Benefits and Practical Applications

CAD’s near‐universal response regardless of analyte structure facilitates accurate quantitation when pure impurity standards are missing. The approach enhances mass balance accuracy in stability‐indicating assays and routine QA/QC of APIs.

Future Trends and Potential Uses

Future developments will likely integrate CAD with advanced HPLC platforms for automated inverse gradient control. Extensions may include broader nonvolatile compound classes and coupling with high‐resolution separations for complex matrices.

Conclusion

CAD combined with an inverse gradient HPLC approach delivers superior sensitivity and uniform response compared to ELSD and UV. This method streamlines impurity quantitation and mass balance studies in pharmaceutical analysis.

Reference

• ICH Q1B: Photostability Testing of New Drug Substances and Products (1996)
• ICH Q1A(R2): Stability Testing of New Drug Substances and Products (2003)
• ICH Q2A: Validation of Analytical Procedures – Text for Validation (1994)
• ICH Q2B: Validation of Analytical Procedures – Methodology (1996)
• Gorecki T., Lynen F., Szucs R., Sandra P. Universal Response in Liquid Chromatography Using Charged Aerosol Detection. Anal. Chem. 2006, 78 (9), 3186–3192.
• ESA Application Note 70-8913