Jack G. Saad, part of the Scientific Services group specialized in particle sizing, recently presented at the 2013 American Society of Brewing Chemists (ASBC) Conference in Tucson, AZ. The presentation, entitled “the particle size paradox,” was given before an audience of food scientists in the beverage industry.
Based on literature and conversations with attendees, particle sizing applications of interest include:
- Use of Electrical Sensing Zone (Elzone) for yeast counting, particulate counting, and cleaning validation.
- Use of Dynamic Image Analysis (Particle Insight) for shape and size analysis of diatomaceous earth used in filtering.
- Using Dynamic Light Scattering (NanoPlus AT) for nanobubble formation studies for controlling gushing of carbon dioxide in the presence of hydrophobins.
- Using Static Light Scattering (Saturn) for general particle sizing applications in food science, like flour.
Particle sizing is a unique analytical tool that is technique dependent. The researcher must define what they consider a particle in order to prepare a sample appropriately for analysis. Aggregated or agglomerated particles may give information on the processing of the material. Once a definition of particles is determined, the researcher must understand the definition of size. Typically, “particle size” refers to the diameter of a particle, but can also be expressed in terms of volume or surface area. The “paradox” of particle sizing is that different techniques will yield different size values and all are correct. Particle sizing is technique dependent and is calculated from a unique characteristic measurement of the particle.
Dynamic Image Analysis measures linear and two-dimensional values and reports particle size using various definitions including equivalent spherical diameter.
Sedimentation Analysis measures settling velocity and reports equivalent spherical diameter using Stokes’ law.
Static Light-Scattering Analysis measures light intensity at various angles and reports equivalent spherical diameter using Mie theory.
Electrical Sensing Zone Analysis measures changes in resistance and reports volume and equivalent spherical diameter using the Coulter Principle.
When comparing particle size data collected by two different techniques, it is extremely rare to simply convert to equivalent spherical diameter and find agreement. Therefore, when communicating particle size, the measurement technique is an important quality to include. Furthermore, including information about particle shape also is advisable, especially if the size data are to be compared to results from another technique.
The reported size is technique-dependent-there is not a definitive particle sizing technique.
To view the full presentation, please click the following links:
Micromeritics Instrument Corp./Particulate Systems Booth at 2013 ASBC:
Additional application reading using Electrical Sensing Zone: