Size distribution and particle morphology of analytes dried through the Evaporative Light Scattering Detector: Part A

Abstract. This study investigates the size distribution and particle morphology of analytes dried through an Evaporative Light Scattering Detector (ELSD), a widely used detector based on aerosol light scattering in pharmaceutical and materials analysis. We employed multiple particle sizing techniques, including a Phase Doppler Particle Analyzer (PDPA), Aerodynamic Aerosol Classifier (AAC), and Scanning Mobility Particle Sizer (SMPS), to characterise droplet and particle distributions at various stages within the ELSD. Initial droplet size distributions were reconstructed using dioctyl sebacate (DOS) as a non-evaporating surrogate and correlated to water droplets. Downstream particle measurements were conducted for caffeine, dextran, and citric acid at different concentrations and operating conditions. Scanning Electron Microscopy (SEM) was used to examine dried particle morphology. Results show that analyte properties significantly influence final particle size and morphology, with implications for ELSD signal and detection detection. This is the first comprehensive characterisation of the particle drying and scattering process within an ELSD, and provides both physical insight in its operation, as well as data for the validation of a model.