Is there a “right” particle size and shape measurement tool?: A comparative study of seven online and offline devices on nine different particle populations

Accurate characterization of the particle size and shape distribution (PSSD) of particle ensembles is essential for effective design, modeling, and control of crystallization processes. Despite the wide range of techniques available for the measurement of PSSDs, there is a noted gap in the literature concerning a comparative analysis of these methods when characterizing PSSDs. To this end, five commercial and two bespoke techniques were used to characterize nine particle ensembles. The evaluated instruments include Mettler Toledo’s FBRM and EasyViewer, BlazeMetrics’ probe, Malvern’s Laser Diffraction and Morphologi; alongside a stereoscopic imaging device (DISCO) and a confocal microscopy device (Petroscope). Test samples include small, medium, and large spherical glass beads with known size ranges; small and large sodium chloride cubes obtained through sieving; two populations of needle-like d-mannitol crystals; plate-like adipic acid crystals; and agglomerated l-Glutamic acid crystals. The results show that online devices generally disagree with each other, with offline devices, and with independent size references such as sieve fractions. For equant particles, offline devices exhibit good agreement with each other and independent size references. However, discrepancies arise for non-equant crystals (i.e. needles, plates). Only the Morphologi, DISCO, and Petroscope offer 2D characterization (length and width), while only the non-commercial bespoke techniques, i.e. DISCO and Petroscope, provide 3D characterization (length, width, and thickness). Comparing the measured PSSDs reveal small differences between the two bespoke devices. The outcomes from this study will inform practitioners on the strengths and limitations of PS(S)D characterization techniques and in turn their selection for specific applications.