What is Particle Size Analysis?

Particle size analysis is a fundamental analytical technique used to determine the size distribution of particles within a sample. It is a core activity in sectors such as pharmaceuticals, chemicals, materials science, food production, cosmetics, and environmental research, where particle behaviour has a direct impact on quality and performance. Whether a company is developing a new formulation, validating a production batch, or studying the behaviour of complex materials, particle size measurement provides data that supports more reliable technical decisions.
In practical terms, particle size analysis helps researchers and manufacturers understand how a material will behave during formulation, storage, processing, and final use. Powders, emulsions, suspensions, colloids, and biological samples can all show very different properties depending on their particle size and distribution. This is why particle characterization is not simply a laboratory exercise, but a strategic analytical step that supports innovation, quality control, and product consistency.

Why Particle Size Matters

Particle size directly influences a wide range of physical and chemical properties, including surface area, solubility, dissolution rate, stability, sedimentation, and reactivity. In pharmaceutical applications, for example, smaller particles may dissolve more quickly and improve drug bioavailability, while larger or more heterogeneous particles can change release profiles or reduce formulation stability. In other industries, the same principle applies: the way particles are distributed within a sample can determine how the entire product performs.
In industrial applications such as coatings, inks, pigments, and abrasives, particle size affects colour intensity, texture, optical properties, mechanical resistance, and processability. Even small changes in size distribution can create major differences in final product quality, especially when consistency is critical. This is why companies invest in accurate particle size analysis: it reduces variability, improves process control, and helps avoid quality issues before they become commercial problems.

Main Techniques for Particle Size Analysis

Several analytical techniques are available for particle size analysis, and each method offers advantages depending on the sample and the level of detail required.

We can identify three main categories:

• Ensemble methods: many particles are measured at once. Particle sizes are retrieved by statical means. For example, Dynamic Light Scattering (DLS), laser diffraction as Static Light Scattering (SLS) and Multi Angle Light Scattering (MALS).
• Single Particle methods: single particles are measured individually. These methods typically provide concentration values alongside particle’s sizes. In this category there are Light Obscuration / Single Particle Optical Sizing (SPOS), Single Particle Extinction and Scattering (SPES), Nanotracking Analysis (NTA), Coulter Counter.
• Imaging methods, for particles from 1 um or above only. Besides traditional microscopy techniques, Flow Imaging Microscopy (FIM) allows to automatic measure entire samples and perform image analysis on large datasets.

Laser diffraction is one of the most widely used techniques because it can cover a broad particle size range and provide fast, repeatable measurements for many industrial applications. It measures the angular pattern of light scattered by a particle ensemble and computes its Particle Size Distribution (PSD) by using a theoretical model – typically Mie or Fraunhofer. The retrieved PSD is based on the assumption that all particles in the ensemble are homogeneous sharing the same shape and optical properties, where individual particles are considered equivalent and differ only in size, not in internal structure or composition. It covers a very broad range, spanning from sub-um to mm sizes, retrieving quickly PSDs. Widely adopted in ISO environments and Quality Control.

Dynamic Light Scattering, or DLS, is typically used for nanoparticles and colloidal systems, with sub-micron dimensions. DLS infers particle size from the Brownian motion driven fluctuations in scattered light intensity; the diffusion coefficient is converted to hydrodynamic diameter using the Stokes–Einstein equation. DLS measures the hydrodynamic radius rather than the actual size of the particles. It’s a fast technique that excels measuring nanoparticles and sub-micron particles. On the other hand, it suffers from sedimentation of larger or heavier particles, whose motion is not Brownian. It cannot provide absolute concentration measurements and differentiate particles of different materials with the same hydrodynamic behavior.

Single Particle Optical Sizing (SPOS) and Light Obscuration are similar single particle technologies that provide concentration and size distribution of particles in a liquid using a combination of extinction and scattering measurements. It measures individual particle transits in diluted liquid samples. Particle size is inferred via instrument calibration with reference particles, implying that sizing accuracy depends on the assumption that all measured particles behave optically like the calibration standard. LO in the standard in Injectables following the USP 788 norm. These methods excels in measuring rare events and outliers.

NTA (Nanotracking Analysis) uses the same theory behind the DLS but applied to video analysis of light scattered by nanoparticles, of which it can retrieve their hydrodynamic radius. At variance with DLS, it tracks single particles without doing ensemble averages.

Coulter Counter are electrical-sensing techniques that measure a difference in the impedance of a small aperture when particles immersed in a electrolyte pass through. They do not measure optical properties but rather the volume of single particles. Particle size is inferred via instrument calibration with reference particles, implying that sizing accuracy depends on the assumption that all measured particles behave like the calibration standard. SPES technology (Single Particle Extinction and Scattering) goes a step further by performing a multiparametric optical measurements, at a single particle level.
For each particle the real and imaginary part of the scattered electric field is retrieved. This allows to obtain not only the size but also the effective refractive index of the particles. In this overview, it’s the only technique capable of measuring the refractive index and also the most suited to separate different populations in complex mixtures, thanks to a combination of differences in size and refractive index. It provides numerical concentrations of each subpopulation in complex samples and is best suited when valuable data and a complete understanding of the sample is required – often the case in R&D and academic research.

Applications Across Industries

Particle size analysis is used across a wide range of industries because particle behaviour affects both technical performance and business outcomes. In pharmaceuticals, it supports drug formulation, delivery system development, and quality control by helping teams understand how particles interact in suspensions, emulsions, liposomes, and other complex systems. In materials science, it is essential for the development of advanced materials, where particle size can influence mechanical strength, reactivity, and functional behaviour.

Beyond research, particle size analysis plays an important role in industrial production. It is used in pigments and inks to optimize colour consistency and dispersion, in food and beverage applications to control texture and stability, and in abrasives and slurries to improve process performance and product reliability. Because each sample type presents different challenges, the choice of analytical method must be aligned with both the material characteristics and the application goals.

How to Choose the Right Method

Selecting the right particle size analysis method depends on a combination of factors, including the particle size range, sample concentration, optical properties, level of heterogeneity, and the type of information needed from the analysis. A routine quality control process may prioritize speed and reproducibility, while a research-driven application may require deeper characterization and the ability to distinguish between different particle populations within the same sample.

This is where method selection becomes a strategic decision. Traditional techniques are often suitable for simpler systems, but complex samples may require more advanced analytical approaches. Technologies such as SPES are especially useful when a laboratory needs to go beyond average values and understand the real composition of heterogeneous particle systems. Choosing the correct method improves data quality, shortens development time, and ensures that analytical results actually support the intended application.