title: Retention mechanism of a cholesterol-coated C18 stationary phase: van't Hoff and Linear Solvation Energy Relationships (LSER) approaches.
abstract: This study examines the effect of temperature on the dynamic cholesterol coating of a C18 stationary phase and the effect of this coating on the retention mechanism. In general, an increase in temperature results in a decrease in the mass of cholesterol coated on the stationary phase. Typically, an increase in temperature from 25°C to 55°C results in a nearly 60% reduction in the mass of cholesterol loaded. The inclusion of temperature, along with loading solvent composition and cholesterol concentration in the loading solvent, allows for loading a targeted amount of cholesterol on the stationary phase over an order-of-magnitude range. In addition to loading studies, the retention mechanism of small non-ionizable solutes was examined on cholesterol-coated stationary phases. A van't Hoff analysis was performed to assess retention thermodynamics, while a LSER approach was used to examine retention mechanism. With 50/50 water/organic mobile phases, the addition of cholesterol results in an increase in the entropic contribution to retention, with a decrease in the enthalpic contribution. The opposite trend is seen with 40/60 water/organic mobile phases. LSER system constants are also affected by a cholesterol coating on the stationary phase, with some changing to favor elution and others changing to favor retention.
authors: Department of Chemistry, University of South Alabama, Mobile, AL 36688-0002, USA.
authors: Phillip B
authors: PB
authors: Ogden
authors: Jason W
authors: JW
authors: Coym
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D056148:Chromatography, Reverse-Phase / Q000295:instrumentation / Q000379:methods*; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical; D009930:Organic Chemicals / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D009930:Organic Chemicals; D002784:Cholesterol; D000432:Methanol