Simultaneous enhancement of separation selectivity and solvent strength in reversed-phase liquid chromatography using micelles in hydro-organic solvents.

The role of micelles and organic solvents as the modifiers of the aqueous mobile phase in reversed-phase liquid chromatography (RPLC) in controlling retention and selectivity is discussed. Elution strength increases in RPLC with an increase in organic solvent or micelle concentration. Simultaneous enhancement of separation selectivity with elution strength in the hybrid eluents of water-organic solvent-micelles was observed. This selectivity enhancement occurs systematically, i.e. peak separation increases monotonically with volume fraction of organic solvent added to micellar eluent, and is observed for a large number of ionic and nonionic compounds with different functional groups and for two surfactants (anionic and cationic). For two test mixtures, 13 amino acids/peptides and 15 phenols, it is shown that a better separation and shorter analysis time are observed at stronger hybrid eluents. This selectivity enhancement can be attributed to the competing partitioning equilibria in micellar LC systems and/or to the unique characteristics of micelles to compartmentalize solutes and organic solvents.