Analytical Series – Particle Size Distribution, Measurement, and Assessment – Principles, Features, Limitations, and Benefits

By Theodore Provder

The field of particle size distribution (PSD) character­ization and measurement has experienced a renais­sance over the past 40 years. These changes have been driven by advances in electronics, computer technology, and sensor technology in conjunction with the market pull for PSD methods embodied in cost-effective, user-friendly instrumentation.

These changes can be characterized by at least four activities: (1) End user innovation exemplified by techniques such as hydrodynamic chromatography (HDC), capillary hydrodynamic fractionation (CHDF), and field flow fractionation methods (sedimentation, flow, and thermal fields, respectively SdFFF, FIFFF, and ThFFF);
(2) Revitalization of older instrumental methods s_uch as gravitational and centrifugal sedimentation; (3) Evolution of research-grade instrumentation into low-cost, routine, user­friencUy ins_trumentation exemplified by dynamic light scat­tering (DLS); and (4) The attempt to meet extremely difficult technical challenges such as: (a) providing a single hybrid instrument with high resolution over a very broad dynamic range (4+ decades in size; e.g., Fraunhofer/Mie; photozone sensing/DLS); (b) PSD measurement of concentrated dis­persions (acoustophoretic, dielectric measurements, fiber optic DLS (FOQELS); (c) in-situ process particle size sensors (in-line or at-line, e.g., FOQELS); (d) routine measurement of particle shape and structure (e.g., image analysis). Instrumental methods resulting from these activities are dis­cussed in terms of measurement principles and the strengths and weaknesses of these methods for characterizing PSDs.

Business and societal driving forces will impact customer perceived instrumentation and knowledge needs for the future and the ability to meet the specific difficult technical challenges in particle size distribution characterization mentioned above. Anticipated progress toward meeting these technical challenges in particle size distribution characteri­zation mentioned above is discussed.