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S himadzu offers a broad vari-ety of particle size instru-ments, which support the

well-established laser diffractionmethod, able to cover the meas-urement range of 0.5 nm to 3,000μm. Additionally and exclusivelyShimadzu offers the patented in-duced grating method.

A wide range of accessories en-ables measurements of highly con-centrated, dry or small-volumesamples. The phrases “volumebased particle size distributions”and “number based particle sizedistributions” often appear whendiscussing the results of particlesize measurements.

What is the difference between number and volume based result?

When looking at particle size dis-tributions, “number-based” and“volume-based” change the scal-ing of the y-axis. If not explicitlymentioned, the scaling is “volume-based” as it is the more typicalscaling. But “number-based” isalso quite common.

Here’s the difference: Let’s assumethat a sample solution containsparticles with an average radius of50 μm respectively 100 μm. Theratio of these particles is 1:1.

Dividing 4188790 by 523598 re-sults in 8. So 1:8 is the ratio of thepeaks at 50 μm and 100 μm in theexample above.

In the analysis of an unknownsample containing larger andsmaller particles and “volume-based” analysis is chosen, it ispossible that the peak at lowerparticle sizes cannot be seen. Onthe other hand, it is much easierwhen reporting with a number-based scaling to find the smallestparticles of the sample solution.

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When looking at “number-based”results two peaks will appear: Onepeak is at 50 μm and the second at100 μm. The ratio of these peaks is1:1.

When changing to a “volume-based scaling” the ratio of thesepeaks changes to a ratio of 1:8.The peak at 100 μm is now eighttimes larger in comparison to thepeak at 50 μm.

Here’s the explanation

When looking at number-basedresults, the number of particles istaken into account. At a mixtureof 1:1, the intensity of the lines isself-explanatory.

When looking at volume-basedresults, the volume of the particlesis considered. The software im-plies that all particles are spheresand calculates their volumes ac-cording to

Using particles with 50 μm and100 μm radii (1:1 mixture) resultsin following equations:

10 SHIMADZU NEWS 1/2013

Where’s the difference?Volume-based vs. number-based particle size measurement

Figure 1: Number-based particle size measurement

Inte

nsit

y

Particle diameter

Number-based

1 :1

50 μm 100 μm

Figure 2: Volume-based particle size measurement

Inte

nsit

yParticle diameter

Volume-based

1 :8

50 μm 100 μm