Dynamic Light Scattering by Zetasizer, Malvern / DynaPro, Wyatt / NanoFlex, Particle Metrix
Dynamic light scattering (DLS) is a sizing technique for particles, proteins, colloids and dispersion, with wide delectable range from 0.5 nm to 10 um. The measured scattered light intensity generated by sample allows determine particle size, molecular weight and zeta potential.
Small particles in a dispersion or solution are subject to Brownian motion. DLS is driven by collisions with the solvent molecules present, which are in constant movement due to their thermal energy. The speed of Brownian motion can be directly measured from the scattered light pattern produced by the moving particles, a technique known as photon correlation spectroscopy (PCS) or quasi-elastic light scattering (QELS) but presently referred to as DLS. The relationship between the speed of Brownian motion of a particle and that particle’s size is defined by the Stokes-Einstein equation.
The benefits of DLS are:
Small sample volumes: 20uL - 1 mL.
Wide delectable range from 0.5 nm to 10 um
Measure both dilute and turbid systems with the concentration range for analysis reaching down as low as 0.1ppm and up to 40% w/v.
The limitations of DLS are:
Large particles if present in even small quantities may be accounted during data analysis.
Sedimentation for dense particles.
Low resolution. DLS will not precisely characterize a polydisperse sample, making it advisable to apply separation prior to measurement.
Multiple light scattering - Multiple scattering is when the scattered light from one particle is scattered by another before reaching the detector, and it compromises the accurate calculation of particle size in more concentrated samples.
Dispersant choice – Even though most dispersants are suitable, those with a viscosity greater than 100 mPa*s inhibit reliable measurements. Furthermore, light absorption by the dispersant can interfere with detection