A simplified tutorial on charged aerosol detection: Understanding the basics, optimization, and troubleshooting

• Optimization of the power function value improves CAD linearity • Proper use and maintenance ensures quality and reliability of CAD • Monitoring historic performance of CAD and proper troubleshooting minimizes downtime • Use of inverse gradient minimizes analyte-to-analyte variability The charged aerosol detector (CAD) is an instrument that measures the overall charge deposited on aerosolized particles to produce a signal related to the mass of analyte present. This applies to compounds with or without a chromophore. A significant benefit of CAD is the ability to quantitate a wide range of non-volatile compounds in absence of their authentic standards due to uniform response factor for such analytes. CAD is also a valuable tool to help detect and/or quantitate compounds with poor or no UV absorption. These can include salts, impurities, and a variety of other types of analytes. In this tutorial, fundamental principles of CAD and its utilization, troubleshooting, and maintenance will be demonstrated to ensure proper CAD usage. Successful operation of CAD includes optimizing power function value (PFV) to allow for a broader dynamic range and improve uniformity of response. The use of an inverse gradient (admixed post-column) enables more accurate quantitation, when employing a gradient analysis method. Several troubleshooting strategies, including diagnosing inverse gradient pump organic solvent delivery and determining volume match/mismatch between the inverse gradient and system pumps, will be presented and are important aspects of operating a CAD. Lastly, ensuring reliable results involves monitoring the performance of CAD over time to understand whether it is working sufficiently or if maintenance is required.