Partitioning of small organic molecules in aqueous biphasic systems.

Aqueous biphasic systems (ABS) are suitable for the separation of small organic molecules in industrial and environmental applications and thus, it is important to correlate partitioning behavior of model organic solutes with their structure in order to develop predictive models. The partitioning behavior of five, uncharged, substituted benzenes (benzene, toluene. chlorobenzene, 1,4-dichlorobenzene and 1,2,4-trichlorobenzene) were studied in ABS prepared from stock solutions of 40% (w/w) PEG-2000 and increasing concentrations of four water-structuring salts (K3PO4, K2CO3, (NH4)2SO4 and NaOH). For a given solute and a defined concentration of salt, the partition coefficients increase as the deltaGhyd value of the salt anion becomes more negative (e.g., Dbenzene increases in the order OH- <SO42- <CO32- <PO43-). In a given salt, the distribution ratios increase in the order benzene<toluene<chlorobenzene< 1,4-dichlorobenzene< 1,2,4-trichlorobenzene. The partitioning behavior of the solutes in PEG-salt ABS was found to be strongly correlated with their partitioning coefficients in 1-octanol-water biphasic systems.