title: Characterization of C18-bonded liquid chromatographic stationary phases by Raman spectroscopy: the effect of temperature.
abstract: This study represents the first time that both the mobile phase composition and the temperature are simultaneously controlled to examine silica-bonded octadecylsilyl (C18) ligands spectroscopically at typical liquid chromatographic (LC) mobile phase flow-rates and back-pressures. Raman spectroscopy is used to characterize the behavior of the C18 bonded ligands equilibrated at temperatures from 45 to 2 degrees C in neat, single-component, mobile phase solvents including: water, acetonitrile, methanol, and chloroform. In addition, the effect of stationary phase ligand bonding density is examined by using two different monomeric reversed-phase liquid chromatographic (RPLC) stationary phases, a 2.34 and a 3.52 micromol m(-2) Microporasil C18 stationary phase, under identical conditions. The direct, on-column, spectroscopic analysis used in this study allows direct evaluation of the temperature-dependent behavior of the bonded C18 ligands. The temperature-dependent ordering of the stationary phase ligands is examined to determine if the ligands undergo a phase transition from a less-ordered "liquid-like" state at higher temperatures to a more-ordered "solid-like" state at lower temperatures. A discrete phase transition was not observed, but rather a continual ordering as temperature was lowered.
authors.affiliation: Department of Chemistry, University of Cincinnati, OH 45221-0172, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Doyle
authors.forename: T J
authors.initials: TJ
authors.lastname: Vickers
authors.forename: C K
authors.initials: CK
authors.lastname: Mann
authors.forename: J G
authors.initials: JG
authors.lastname: Dorsey
mesh_terms: D002853:Chromatography, Liquid / Q000295:instrumentation*; D008968:Molecular Conformation; D013059:Spectrum Analysis, Raman; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water