Water-immiscible solvents as diluents in reversed-phase liquid chromatography.

It has recently been shown that the use of strong organic solvents as diluent is possible in RPLC, provided that the solvent used as diluent is retained more strongly by the column than the analytes in the sample. In this study, the phenomenon was further studied experimentally using several water-immiscible solvents (ethyl acetate, isopropyl acetate, and methyl isobutyl ketone) and several model analyte compounds. In all cases, analyte peak distortion was minimal provided the analyte eluted earlier than the diluting solvent, in contrast to substantial broadening and distortion when the analyte eluted after the diluting solvent. The potential analytical utility of this approach is discussed, and an example of a practical application is also presented.