I have some questions about DLS (Dynamic light scattering). Does this method give the concentration of the particles in the suspension? Is there any limitation in the percentage of the particles to the quantity of liquid?
Hi Navideh,
Dynamic light scattering measures diffusion coefficient which can be converted into particle size.
As part of the measurement, scattering intensity is also recorded and traditionally this may have been used against a calibration curve to estimate concentration.
In terms of limitations for concentration, this is sample dependent but the limiting factors are number fluctuations at low concentration and multiple scattering at high concentrations.
Number fluctuations is where the average scattering is not consistent because the number of particles in the detection volume is changing significantly over time, and multiple scattering will skew results at high concentration if the incident light scatters off of more than one particle before being detected.
Traditionally optically clear samples would be used for DLS, however instruments that allow variable path lengths can be used at higher concentrations and measure turbid samples reliably.
The Zetasizer Ultra can perform a particle concentration measurement which uses a high resolution size measurement (using Multi Angle DLS) and the detected scattering to calculate a particle concentration in particles/ml.
https://www.malvernpanalytical.com/en/learn/knowledge-center/technical-notes/TN180720ParticleConcZetasizerHowTo.html
https://www.malvernpanalytical.com/en/learn/knowledge-center/whitepapers/WP180926ImprovedComponentResolutionMADLS
Unfortunately, unlike Beer-Lambert's law where absorbance is directly proportional to concentration (within the limit of the law) scattering does not follow a similar relation.The extent of scattering(intensity) is directly proportional to the size. Implying, scattering will provide information about what size ranges your sample contains.
An excellent example of this limit of DLS is the following paper by Professor Shibayama
Article Formation of Clusters in Whiskies During the Maturation Process
In this paper they show that there is a distribution of two types of particles through DLS, but to obtain the concentration or the ratio of concentration they perform X-ray scattering and fit that data to a certain equation so as to obtain concentration from the pre-factors.
Long story short, DLS will tell you the types of particles in your suspension/solution,but will not tell you the ratio in which they are. You need additional or other techniques for the same.
Good luck!
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