Validating Analytical Methods with Charged Aerosol Detection

Significance of the Topic

Universal detection technologies such as charged aerosol detection (CAD) are increasingly valuable in regulated analytical environments due to their broad applicability beyond UV-active compounds. Developing robust, validated methods that combine CAD with orthogonal detectors addresses challenges of matrix interference, multi-component analysis, and stringent reproducibility requirements.

Study Objectives and Overview

The study aimed to review peer-reviewed CAD applications and to develop and validate an HPLC-UV-CAD approach for simultaneous quantification of naproxen (API) and its counterion (sodium) released from tablet dosage forms. Specific goals included reducing runtime, eliminating matrix effects, and meeting accuracy, precision, and detection limit criteria in a dissolution matrix containing Tween® 80 and formic acid.

Methodology

• Tablet dissolution in Tween 80/formic acid/water for up to 4 h with periodic sampling at 1, 2, and 4 h
• Filtration (0.22 µm nylon) and dilution (up to 10×) in acetonitrile/water before analysis
• HPLC configuration:

• Dual-gradient pumps with two trap C18 columns in tandem for matrix removal
• Mixed-mode Acclaim Trinity™ P1 column for simultaneous reversed-phase and ion-exchange retention
• Flow switching via a 10-port, 2-position valve to minimize cycle time

• Mobile phases:

• Pump Right: acetonitrile, water, ammonium acetate buffer (pH 4.5)
• Pump Left: acetonitrile, isopropanol, water

• Injection volume: 10 µL; total run time per cycle: 15 min

Instrumentation

• Thermo Scientific Dionex UltiMate™ 3000 RSLC system with DGP-3600RS dual ternary pump, WPS-3000TRS sampler, TCC-3000RS column compartment, and DAD-3000RS diode array detector
• Thermo Scientific Dionex Corona ultra™ CAD (neb temp 25 °C, high filter)
• Acclaim RSLC C18 trap columns (3.0×33 mm) and Acclaim Trinity™ P1 analytical column (3.0×50 mm)

Key Results and Discussion

• Separation of naproxen and sodium achieved in under 5 min, full cycle 15 min vs 60 min for a single-stream method
• Limits of detection (LOD): sodium ~0.75 ng (CAD), naproxen ~5 ng (CAD) and ~1.5 ng (UV)
• Calibration models: linear CAD response for sodium (100–175 ng), second-order polynomial for broader range; UV linear for naproxen
• Accuracy: sodium 99.85% (±0.82 % RSD); naproxen 101.6% (±2.1 % RSD)
• Precision: intra- and interday RSD <3% for CAD-detected sodium and UV-detected naproxen
• Tablet recovery: sodium within 97–103%; naproxen recovery fell below target due to solubility/matrix limitations
• Matrix interference: minor early peaks in CAD trace; UV detection remained specific for naproxen at 254 nm

Method Benefits and Practical Applications

• Combined CAD and UV detection allows universal counterion quantification alongside UV-active APIs without method duplication
• Tandem trap columns and valve switching significantly reduce cycle time and extend column lifetime by removing surfactant matrix
• High reproducibility and accuracy meet regulatory validation criteria for specificity, linearity, precision, and limits of detection
• Practical for pharmaceutical QA/QC testing of dosage forms requiring simultaneous analysis of ionic and non-ionic species

Future Trends and Potential Applications

• Integration of CAD with mass spectrometry for enhanced compound identification in complex matrices
• Development of new column chemistries to further mitigate surfactant and lipid interferences
• Advanced calibration algorithms (e.g., machine learning) to improve non-linear detector quantification precision
• Automation and inline sample preparation to increase throughput in regulated laboratories

Conclusion

By combining a mixed-mode analytical column, rapid valve-switching pump configuration, and dual detection (CAD and UV), the validated method achieves high throughput, robust accuracy, and precision for simultaneous API and counterion analysis. Early investment in method optimization and realistic validation criteria ensures regulatory compliance and operational efficiency.

References

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