Table of contents 1 Why is particle size important?

IMAGE ANALYSIS
The primary result reported by image analysis is a number distribution since the 
particles are inspected one at a time. Setting specifications based on the number
distribution is acceptable, but this is the one example where conversion to another 
basis (i.e. volume) is both acceptable and often preferred. As long as a sufficient
number of particles are inspected to fully define the distribution, then the conversion
from number to volume does not introduce unknown errors into the result. The 
pharmaceutical industry discussed the subject at a meeting organized by the AAPS 
(ref. 6) and concluded that results are preferably reported as volume distributions. 
Particle size distribution specifications based on the image analysis technique often
include the mean, D10, D50, and D90 values. Care should be taken to avoid basing 
specifications on the number-based mean since this value may not track process
changes such as milling or agglomeration (ref. 12). Conversion from number to 
volume distribution can be performed with high accuracy by specifying the typical 
particle shape (spherical, cylindrical, ellipsoidal, tetragonal, etc.). 
Particle shape parameters such as roundness, aspect ratio, and compactness are 
used to describe particle morphology. Specifications for shape parameters are
typically reported using just the number-based mean value, so this is recommended 
for setting specifications.
CONCLUSIONS
The task of setting a particle size specification for a material requires knowledge
of which technique will be used for the analysis and how size affects product 
performance. Sources of error must be investigated and incorporated into the final
specification. Be aware that, in general, different particle sizing techniques will
produce different results for a variety of reasons including: the physical property 
being measured, the algorithm used, the basis of the distribution (number, volume, 
etc.) and the dynamic range of the instrument. Therefore, a specification based on
using laser diffraction is not easily compared to expectations from other techniques 
such as particle counting or sieving. One exception to this rule is the ability of 
dymanic image analysis to match sieve results. 
Attempting to reproduce PSD results to investigate whether a material is indeed 
within a stated specification requires detailed knowledge of how the measurement
was acquired including variables such as the refractive index, sampling procedure, 
sample preparation, amount and power of ultrasound, etc. This detailed information 
is almost never part of a published specification and would require additional
communications between the multiple parties involved.
14

RANGE IN MICRONS
10nm - 3,000 (5mm)
OPTIMAL APPLICATIONS
POWDERS, SUSPENSIONS,
AND EMULSIONS 
WEIGHT 
56kG (123 lbs)
FOOTPRINT
WIDTH 705mm (28”)
DEPTH 565mm (22”) 
HEIGHT 500mm (20”)
LASER 
DIFFRACTION 
TECHNIQUE

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