How To Select A Particle Size Analyzer

Introduction

Particle Size Analysis is an analytical technique by which the distribution of sizes in a sample of solid or liquid particulate material is measured and reported. Particle size analysis is an important tool in characterizing a wide range of final-product performance factors.

Numerous analytical techniques and approaches exist for particle size analysis. Particle size analyzers range from the historical sieve to modern automated light scattering instruments. The most appropriate selection for a particular application depends on a number of factors including the size range of interest, nature of the sample, the information required from the analysis, the analytical method, and sample throughput.

Selecting the most appropriate instrument for a given application depends on a number of variables. The user must determine those factors that are most important for their application when considering the multitude of alternative particle sizing techniques and models. This page reviews key considerations in choosing a particle analysis technique.

Below is a list of considerations that should be addressed before a technique is chosen

  • Current analysis technique or practice
  • Size range
  • Chemistry or Material
  • Desired information
  • Desired throughput
  • Amount of sample available for analysis.
  • Budget

Each of these points is discussed in more detail below.

Current analysis technique or practice

The choice of particle size analyzer often depends on previous experience. For example, knowing the sample size range requires some sort of size analysis, even if it is simply looking at a few particles under a microscope or rubbing them between your fingers to feel them. Understanding the current technique will help clarify expected results or new needs.

Often, there is a body of literature or practice that will guide the decision making process. For example, a manufacturing plant may already have a size analyzer and they are looking for an improvement. Or, the scientific literature may be dominated by results from one technique.

It is also useful to think about the importance of correlation to past results. For example, some manufacturers need to match historical sieve data or laser diffraction data in order to ensure they do not upset their customer’s processes. Many find that an updated technique allows them to escape old analytical problems such as poor resolution and do not want any correlation. 

Size Range

To choose between different techniques, the size range is usually the prime factor. The chosen technique should identify not just the median size, but the full range of sizes in the distribution. In cases where more than one instrument covers the desired size range, consider other possible samples and possible future developments. For example, a new product with a larger particle size may be introduced in the future. This may suggest that the analyzer with the higher upper size limit is a better choice than an analyzer with a smaller lower size limit. Figure 1 below shows the size ranges of some techniques.

A note of caution: The stated size range for an analyzer does not apply for all samples and all cases. Choosing an analyzer such that the particle size of the sample is in the middle of the instrument size range is almost always wise. In general the data is better and you are better able to work with variations in particle size about your expected value.

image analysis: 1 micron to 30 mm
Figure 1: Approximate size ranges of common particle sizing techniques.

Analytical Technique

Modern static light scattering instruments have become the method of choice in most industries due to

  • the analysis speed (approximately 30 seconds)

  • wide size range

  • ease of use
  • flexibility
  • reproducibility

The somewhat higher cost is balanced by their greater productivity that traditional methods and tighter control on production processes. For quality control applications, the entire process can be automated, eliminating operator error and providing consistent feedback. The Partica LA-950 is the highest capability model in HORIBA's range, with a full range of accessories.

Digital image processing is capable of providing shape information, a critical parameter for materials where the particle length, aspect ratio, sphericity, or other shape parameter is important to final product performance. The Camsizer is the instrument of choice for these applications.

Dynamic light scattering is most appropriate for smaller size ranges, and the new SZ-100 has the advantage of being able to perform sizing measurements at two angles (90 degrees and backscatter) to extend the detection range from 0.3 - 8,000 nanometers.

Sample Requirements

Different analytical techniques allow the use of different accessories or sampling systems that may be more appropriate for the material of interest. They may also be more sensitive to a particular product parameter than other techniques. Consultation with the vendor's experts will help in determining the most appropriate selection.

For example, a fragile agglomerated powder or highly-soluble material would be best analyzed as a dry powder by static light scattering instruments. Materials with limited availability or that are toxic or expensive would require a small volume measurement cell available with several different analyzer systems. Samples that are sensitive to dilution would require analyzers like the SZ-100 to measure at higher concentrations.