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Jack G. Saad, a member of the Scientific Services group specializing in particle sizing, presented at the 2013 American Society of Brewing Chemists (ASBC) Conference in Tucson, AZ. The title of the presentation was “The Particle Size Paradox,” and was presented in front of an audience of food scientists in the beverage industry.
The main particle sizing applications of interest are:
- Use of electrical sensing (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, such as sizing flour.
Particle sizing is a unique technique-dependent analytical tool. The researcher should first define what they consider a particle for preparing a sample correctly for analysis. Agglomerated or aggregated particles may offer information on material processing.
On determining the definition of particles, the researcher should understand size definition. Typically, “particle size” refers to the diameter of a particle, but can also be expressed in terms of volume or surface area.
Particle sizing is such that using different techniques result in different values of size and are correct. Particle sizing is based on the technique and is determined from a unique characteristic measurement of the particle.
Techniques for Particle Sizing
The common methods of particle sizing are:
- Dynamic image analysis - determines linear and two-dimensional values and reports particle size using various definitions including equivalent spherical diameter.
- Sedimentation analysis - determines 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 - determines changes in resistance and reports volume and equivalent spherical diameter using the Coulter Principle.
While comparing particle size data collected by two different techniques, it is very rare to simply convert to equivalent spherical diameter and find agreement. Hence while communicating particle size, the measurement technique is a very important quality to include.
Including information about particle shape is also advisable, especially if the size data is to be compared to results from another technique. The reported size is technique-dependent - there is not a definitive particle sizing technique.
This information has been sourced, reviewed and adapted from materials provided by Micromeritics Instrument Corporation.
For more information on this source, please visit Micromeritics Instrument Corporation.