Charged Aerosol Detection 101

Significance of Charged Aerosol Detection

Charged aerosol detection (CAD) has emerged as a universal and mass-sensitive detector for liquid chromatography, enabling quantification of non-volatile and semi-volatile compounds without the need for chromophores or ionizable groups. Its uniform response across a wide range of chemical structures and high sensitivity make it indispensable for applications in pharmaceuticals, biopharma, food analysis and quality control laboratories.

Objectives and Study Overview

This work reviews the fundamentals of CAD, compares its performance to evaporative light scattering detection (ELSD), traces the evolution of CAD instruments and highlights representative applications. The aim is to demonstrate CADs advantages in dynamic range, sensitivity, calibration flexibility and practical workflows.

Methodology and Used Instrumentation

The CAD workflow involves:

• Nebulization of the LC eluent via a concentric aerosol generator (FocusJet).
• Evaporation of mobile phase in a heated chamber, leaving analyte particles intact.
• Diffusional or corona charging of particles in a mixing chamber.
• Collection of charged particles in an ion trap and measurement by an electrometer.

The main instruments discussed include Thermo Scientific Dionex Corona Plus, Corona Ultra RS, Corona Veo RS and Vanquish charged aerosol detectors, integrated with HPLC, UHPLC and micro-LC platforms.

Main Results and Discussion

CAD offers a linear dynamic range exceeding four orders of magnitude and limits of detection below 1 ng on column for non-volatile analytes, outperforming ELSD in sensitivity and calibration range. Response is essentially independent of compound polarity or size, enabling relative quantitation without analyte-specific standards. Representative examples include aminoglycoside antibiotics, drug counterions, excipients, degradation products and food constituents such as sugars, lipids and sweeteners. Combined UV and CAD detection provided complementary selectivity, while single-detector CAD methods simplified impurity and stability assays.

Benefits and Practical Applications

• Universal detection of compounds lacking chromophores or chargeable groups.
• Wide dynamic range and low detection limits down to sub-ng levels.
• Uniform response enabling relative quantification without analyte reference standards.
• Compatibility with gradient HPLC, UHPLC and micro-LC workflows.
• Application in drug composition, formulation (counterions, surfactants), stability testing, glycan profiling, cleaning validation, extractables/leachables and food quality control.

Future Trends and Opportunities

Advances in CAD technology may include further miniaturization for nano-flow applications, integration with microfluidic sample handling, enhanced software algorithms for automated calibration and data processing, and expansion to semi-volatile analytes through optimized evaporation strategies. The growing demand for high-throughput QC and online monitoring will drive development of multiplexed and portable CAD systems.

Conclusion

Charged aerosol detection represents a robust, sensitive and truly universal detection method for liquid chromatography. Its independence from optical or ionization properties, combined with broad dynamic range and ease of use, makes CAD a valuable tool for modern analytical laboratories across pharmaceutical, biopharma and food sectors.

References

• Schwahn A. Charged Aerosol Detection 101. Thermo Fisher Scientific.
• Sandra P., Pereira A., David F., et al. J Chromatogr A 1176 (2007) 135–142.
• Thermo Fisher Scientific. Application Note AN20870.