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Comparatively Speaking: Solubility vs. Partition Coefficient
By: Anthony J. O'Lenick Jr., Siltech LLC
Posted: April 10, 2012
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Partition Coefficient is a concept that is a consequence of solubility and relates in that not all of a material will stay in an oil phase or a water phase. The partition coefficient results from most compounds being soluble to some extent in both organic and aqueous phases. The concentration of compound in the two phases is used to determine the partition coefficient.The industry is familiar with using water/ether extraction in a separatory funnel, as illustrated in Figure 2.2 Knowing that some materials partition between hydrophilic (aqueous) and hydrophobic (oil) systems and understanding that this equilibrium is dynamic, allows for the formulation of products in which a material is delivered to the skin from over time from one phase to another. An example is delivery of a material to the skin as it becomes more oily.
The ability to partition compounds into different solvents is important to the cosmetic chemist. There is both oil and water in the skin, and the way actives are distributed into the phases will partly determine the effectiveness of the formulation in the active's delivery.
Reference
1. Solubility, Wikipedia, http://en.wikipedia.org/wiki/Solubility (accessed Apr 11, 2012)
2. Separatory Funnel, Harper College, www.harpercollege.edu/tm-ps/chm/100/dgodambe/thedisk/labtech/sepfun2.htm (accessed Apr 11, 2012)