Hydrophobic Hydroxyapatite

Lopes, M. A., Monteiro, E J., Santos, J. D., Serro, A. P, and Saramago, B., Hydrophobic-ity, surface tension, and zeta potential measurements of glass-reinforced hydroxyapatite composites. /. Biomed. Mater. Res. 45 (4), 370-375 (1999). 

Fractionation is less specific and essentially requires separation efficiency. This is generally performed with ion-exchangers and hydrophobic interaction chromatography, which enable efficient separation by salt or pH gradients. Hydroxyapatite is also a good tool for fractionation where proteins can be separated by both phosphate gradients and sodium chloride gradients. 

Adsorption on finely divided inert materials. These materials offer a large surface area for interaction with protein. Adsorption of protein on charcoal, a nonpolar substance, presumably occurs by hydrophobic interaction and can be used to separate proteins from a fluid matrix. Adsorption on polar substances such as silica, alumina, or hydroxyapatite depends on ionic interactions or hydrogen bonding these substances can be used with buffer elution in chromatographic separations. 

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