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

Electronic spectroscopy of probe molecules provides a powerful means o f characterizing the stationary phase in reversed-phase liquid chromat ography. In particular, both fluorescence and UV-visible absorption sp ectroscopies have been used to characterize these complex interfacial environments. This article reviews the progress made with these approa ches for studying the structure of the stationary phase, the solute en vironment that it produces, and the dynamics of sorbed molecules in re versed-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 in terfaces. Dynamic effects due to excimer formation and quenching are s hown to provide information about hydrocarbon ligand proximity, microv iscosity, and contact of sorbed molecules with the mobile phase. UV-vi sible diffuse reflectances spectroscopy has also been used to characte rize the dipolarity, polarizability and hydrogen bonding interactions of the reversed-phase surface environment. These electronic spectrosco pic approaches lend insight into the organization, orientation, and po larity of the alkyl chains. In this article, the results of these stud ies are reviewed, and their impact on models for reversed-phase retent ion are discussed.