Revisiting large volume injection in non-miscible diluents: an on-line reversed phase supported liquid extraction/liquid chromatography scenario

Abstract

According to some recently published studies, large volume injection (LVI) of diluents immiscible with the eluents used in reversed phase liquid chromatography (RPLC) appears to be feasible, despite the widely accepted rules governing injection related phenomena. The process was previously described and was successfully applied in practice. The present study describes a simple theoretical model explaining LVI of diluents immiscible with the mobile phase in RPLC; the model relies on the on-line coupling of reversed phase supported liquid extraction (RP-SLE) to the chromatographic separation. The compliance of the theoretical model with experimental observations was tested by using data collected for LVI of a homologous series of para-hydroxy alkyl benzoates (methyl, ethyl, propyl, butyl, pentyl, hexyl and octyl congeners) in liquid alkanes (hexane, heptane, iso-octane, decane and dodecane). The SP consisted of an octadecyl chemically modified silica gel eluted with a mixture of acetonitrile : water 4 : 6 (v/v). Although the model mainly focuses on explaining the linear reduction of the retention time with the injected volume, some aspects relating to zone spreading and thermodynamic aspects are also discussed.