Charged aerosol detection and evaporative light scattering detection – Fundamental differences affecting analytical performance

At a fundamental level, both CAD and ELSD share some similarities in that mobile phase exiting the column is first nebulized and then dried to form analyte particles. However, the mechanism by which these techniques measure analyte mass differ markedly and this has major impact on analytical performance. In CAD, charged particles are measured by an electrometer generating a signal that is proportional to particle size (i.e., the mass of analyte). For ELSD, signal is also proportional to particle size, but this relationship is much more complex, as the magnitude of scattered light varies depending on particle size, resulting in sigmoidal response curves. Unlike CAD, ELSD uses non-contiguous signal attenuation. As each attenuation setting has its own unique sensitivity, response, calibration curve and dynamic range, samples may have to be reanalyzed multiple times in order to quantify analytes occurring at different levels. In this poster the analytical performance of CAD and ELSD are evaluated and include: sensitivity, dynamic range, inter-analyte response, linearity, reproducibility and the effects of mobile phase flow rate.