DLS LIMITS

DLS is very sensitive to presence of contaminants, for example organic residues from the lubricant digestion. This is why it is paramount that the particles are purified before any measurement. Furthermore, despite what has been suggested, if the particle size is spread over a wide range (from few nanometer to several tens of micron) the results are highly affected and skewed towards the largest particle. The method is also not capable of distinguishing particles with different chemical composition. Therefore, unless a contaminant has a completely different size distribution it is impossible to distinguish it. Refractive index cannot be used to distinguish contaminants since the particles generally do not have spherical geometry. Furthermore, volume and size are normally calculated assuming a spherical shape (thus based on ECD). Furthermore, laser based techniques are not high-resolution techniques which means they cannot discriminate between particles that have very close size (i.e. 40 and 60 nm will blend into a unique 50 nm band).

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