Nanoparticle Distribution Analysis: DLS or ELS?
Particle size and size distributions (PSD) are key metrics in the analysis of particulate and colloidal samples, from raw materials to finished goods. Increasing the use of particulate materials with sub-microscale (μm) dimensions have placed new demands on testing instrumentation, requiring novel analytical solutions with exceptional sensitivity to nanoscale (nm) particles. A plethora of tools are now available for nanoparticle distribution analysis and characterization, but light scattering is one of the foundational technologies for particle size assessments.
In this blog post, Particulate Systems will compare dynamic light scattering (DLS) and electrophoretic light scattering (ELS) for nanoparticle distribution analysis and explore to what extent these technologies could be considered complementary.
Outlining Nanoparticle Distribution Analysis
Sample dispersity is a measure of heterogeneity with respect to particle size. A monodisperse sample defines a collection of perfectly uniform particles; allowing for nanoparticle size characterizations with a singular measurement. The reality is that most particulates and colloidal samples are polydisperse, consisting of a heterogeneous distribution of particles with different dimensions. This property is statistically generated by advanced software as one of the final processes in the measurement chain.
Nanoparticle distribution is typically displayed as a curve representative of the average particle size in the sample. Various statistical parameters are used to calculate this property depending on the downstream requirements of the data. At its simplest, a nanoparticle distribution may represent the most common particle size in a sample. Refer to our previous blog post for a full breakdown of the basic statistical numbers in particle size distribution analysis.
ELS: An Overview
ELS is an advanced analytical method that measures the electrophoretic mobility of particles in solution, typically as part of zeta (ζ) potential measurements. The velocity of nanoparticles in solution is classically measured using the laser Doppler method which can determine frequency shifts to provide full zeta potential distribution measurements. Alone, ELS is an unsuitable technique for nanoparticle distribution analysis. However, it can provide valuable insights for materials characterization and comparisons under different experiment conditions when integrated with state-of-the-art dynamic light scattering.
DLS: An Overview
DLS is the industry-leading tool for nanoparticle distribution analysis and general size measurements, with the most sensitive measurement range possible (>1 nm). Nanoparticle distribution measurements are conducted by measuring the short-term intensity fluctuations of laser light shone through a sample and analyzing the Brownian motion of nanoparticles according to the Stokes-Einstein relationship. DLS is ideal for particle size ranging on the nanoscale and can be used in isolation to determine extremely accurate nanoparticle distribution ranges. However, combined DLS and ELS capabilities can provide appreciable benefits for establishing and optimizing sample integrity and stability to accelerate product development by eliminating processing challenges at the smallest possible level.
Nanoparticle Distribution Analysis with Particulate Systems
The Zetasizer line of particle analyzers is among the world’s most widely used systems for nanoparticle distribution and size analysis. With combined ELS and DLS capabilities, Malvern Panalytical’s Zetasizer instruments offer rapid, quantitative results with an extremely broad range of parameters, providing unmatched degrees of insight into your product.
Particulate Systems is a global supplier of industry-leading analytical instrumentation. We offer a full Zetasizer range, including:
- Zetasizer Ultra
- Zetasizer Pro
- Zetsaizer Nano Family