Determination of the solvent density profiles across mesopores of silica-C18 bonded phases in contact with acetonitrile/water mixtures: A semi-empirical approach

Core–Shell, Ultrasmall Particles, Monoliths, and Other Support Materials in High-Performance Liquid Chromatography

“…Ionized solutes, which typically show much greater tendency to overload because such solutes must reside inside a small portion of the interface region at a specific distance from the pore wall. Here, the hydrophobic moieties can favorably interact with the C18/acetonitrile mixture closer to the pore wall, while the charged head remains solvated by the water rich bulk eluent at greater distance from the wall …”

“…The fundamental cause of overloading in the porous fraction of shell particles or in totally porous particles on RP materials has been the subject of much debate. Small neutral polar molecules like phenol and caffeine have been proposed to experience weak adsorption sites at the interface between the solvated C18 bonded layer and the bulk eluent, while high energy sites are intercalated deeper within the grafted C18 chains . For charged compounds, the high energy adsorption sites are scarce while their binding constant on the abundant weak adsorption energy sites is low.…”

“…Here, the hydrophobic moieties can favorably interact with the C18/acetonitrile mixture closer to the pore wall, while the charged head remains solvated by the water rich bulk eluent at greater distance from the wall. 67 Small Particles in Capillary Column Format. Much of the driving force for the use of capillary columns in HPLC has come from the positive influence of their low flows on detection methods such as UV and mass spectrometry.…”

Characterization of the Interfacial Liquid Layer Formed on Hydrophobic Packing Material Surfaces by Liquid Chromatographic Analysis of the Distribution of Ions and Molecules

“… 12 Gritti also estimated the thickness of the interfacial region on a C 18 silica surface equilibrated with mixtures of acetonitrile and water using a semiempirical approach based on MD simulation and demonstrated that the interfacial region thickens from 7 to 16 Å as the concentration of acetonitrile increases from 5 to 60%. 45 The values for the thickness of the interfacial liquid layer obtained by our liquid chromatographic method and MD simulations have the same order of magnitude. However, these values for the interface thickness reported by the MD simulation studies may not be compared directly with the L values obtained in this study since the L value gives the average limit of distance from the C 18 -bonded phase surface at which molecules and ions can sense the interfacial liquid layer and it probably involves the thickness of the solvation shell of a probe ion.…”

Organic solvent modifier and temperature effects in non-aqueous size-exclusion chromatography on reversed-phase columns

“…There are three regions that can be distinguished within the chromatographic column [7–9]: ( i ) the solvated bonded-phase region; ( ii ) the interface region, where the ends of the bonded-phase meet the mobile phase; and ( iii ) the bulk mobile phase region. The thickness of the interface region may have a further impact on the pore volume of the column and depends on multiple parameters ( e.g., mobile phase composition, the identity and bonding density of the stationary phase ligands, the morphology of the silica substrate − endcapped or not [10]).…”