ELECTRONIC SPECTROSCOPIC INVESTIGATIONS OF THE STATIONARY-PHASE IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY

Electronic spectroscopy of probe molecules provides a powerful means of characterizing the stationary phase in reversed-phase liquid chromatography. In particular, both fluorescence and UV-visible absorption spectroscopies have been used to characterize these complex interfacial environments. This article reviews the progress made with these approaches for studying the structure of the stationary phase, the solute environment that it produces, and the dynamics of sorbed molecules in reversed-phase liquid chromatography. Fluorescence studies using either covalently attached probes, or physiosorbed probes are reviewed, along with total internal reflection fluorescence studies of flat, model interfaces. Dynamic effects due to excimer formation and quenching are shown to provide information about hydrocarbon ligand proximity, microviscosity, and contact of sorbed molecules with the mobile phase. UV-visible diffuse reflectances spectroscopy has also been used to characterize the dipolarity, polarizability and hydrogen bonding interactions of the reversed-phase surface environment. These electronic spectroscopic approaches lend insight into the organization, orientation, and polarity of the alkyl chains. In this article, the results of these studies are reviewed, and their impact on models for reversed-phase retention are discussed.