Partitioning of L-Tryptophan in Aqueous Biphasic Systems Containing an Alkylimidazolium Ionic Liquid and a Phosphate Salt

For the development of novel liquid extraction systems, systematic experimental data and methods of predicting liquid-liquid equilibria are required. In this work, we report experimental data for a family of aqueous biphasic systems (ABSs) containing 1-butyl- 3-methylimidazolium bromide/chloride, 1-hexyl-3-methylimidazolium bromide/chloride, and 1-methyl-3-octylimidazolium bromide/chloride in the presence of an inorganic salt (K2HPO4 or K3PO4) and assess the predictive capabilities of the ePC-SAFT equation of state in its classical form. The experimental binodal data for eight ABSs have been obtained in a broad concentration range. Although the ePC-SAFT gives a good description of the properties of binary systems, the deviations between experimental and predicted tie lines for the ternary ABSs are significant and the predictions are not quantitative. Improvement in the electrostatic term of the model is required for better performance. We systematically study the partitioning of L-tryptophan, taken as a model solute, and discuss the effect of the alkyl chain length of the imidazolium cation [C(n)mim](+) and the specific effect of the anion of ionic liquids (ILs) (chloride versus bromide). We show that the alkyl chain length of [C(n)mim](+) has almost no effect on the partition coefficients of L-tryptophan (K-Trp) in the ABSs with K3PO4, while lower K-Trp values are found for ILs with the [C(4)mim](+) cation for the ABSs with K2HPO4. A substantial specific effect of the anion of ILs is only observed when the salting-out effect of the inorganic salt is most pronounced, i.e., in the case of the ABSs with K3PO4. It should be specially mentioned that K-Trp values are higher for the ABSs studied in this work in comparison with the available literature data for other IL-salt-water ABSs. This fact implies that the investigated ABSs have high potential for the extraction of biocomponents.

Automated summary

This study systematically investigates experimental data and predictive capabilities of a family of aqueous biphasic systems. Improvements in the model are suggested for better performance. Results show that different chemical compositions affect the partitioning coefficients of L-tryptophan, indicating high potential for the extraction of biocomponents.