Solvent classification for chromatography and extraction

A new method of solvent classification is proposed based on the five system constants of the solvation parameter model for transfer of neutral compounds from the gas phase to solvent and hierarchical cluster analysis for identifying solvents with similar properties and for organizing them into selectivity groups. This method resulted in the classification of 36 common solvents used in chromatography into seven selectivity groups with four solvents (2,2,2-trifluoroethanol, N,N-dimethylformaide, dimethyl sulfoxide, and water) behaving independently. Except for water, the three organic solvents identified as independent are probably a consequence of the lack of other solvents with similar properties in the data set rather than a demonstration of unique solvent behavior. The classification scheme provides a logical approach for solvent selection as the first step in chromatographic method development. A similar approach using the solvation parameter model suitable for the transfer of neutral compounds between condensed phases and hierarchical cluster analysis was used to classify 19 aqueous and 17 totally organic biphasic partition systems for liquid-liquid extraction. The dynamic range of system constants for the aqueous biphasic systems was not great, and selectivity differences were dominated by the high cohesion and strong hydrogen-bond acidity of water. The aqueous biphasic partition systems were classified into three general groups and a fourth dispersed group characterized by high mutual solubility. In contrast, the totally organic biphasic partition systems exhibit an almost continuous range of properties with minimal group formation demonstrating a wider and complementary range of selectivity to the aqueous biphasic systems. The classification of the liquid-liquid partition systems provides a suitable method for the identification of systems for sample preparation based on liquid-liquid extraction and for the simulation of extractions for target compound isolation.