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We present a detailed study on the classification of ZnS quantum dots (QDs) by size selective precipitation (SSP). SSP allows the postsynthetic narrowing of a given feed distribution and is usually realized by titration of a poor solvent into a suspension of dispersed particles. Thereby preferred flocculation of larger structures is induced. Our results confirm that SSP is a highly robust process, following a law of mass action. That means a certain solvent composition always leads to the same ratio between coarse and fines particles with respect to a specific particle size x i . This ratio is independent of the particle size distribution (PSD) of the feed, the washing history of the particles, and the solid concentration of the particles. Regarding the illustration of our findings, we established a combined approach that takes Hansen solubility parameters (HSP) of solvent mixtures as well as changing van der Waals interactions into account. Relating both to each other, a size-dependent region of enhanced solubility is clearly identified. Our concept allows a differentiation between volume-related effects like van der Waals interactions and surface-related effects like the interaction of a ligand with a solvent mixture. A comprehensive interpretation of classification results obtained with different good solvents and poor solvents enables to deduce a general strategy for the demanding determination of HSP for small colloids. Our work makes an important contribution to the design of an appropriate colloidal postprocessing which is applicable to larger quantities.

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