Thermodynamic and kinetic characterization of a bridged-ethylene hybrid C18 stationary phase

Polycyclic aromatic hydrocarbons as test probes to investigate the retention behavior of 1,3-alternate calix[4]arene silica-bonded stationary phases

“…The plots were determined by a least‐squares linear regression method giving correlation coefficients ( r 2 ) > 0.99. A linear Van't Hoff graph indicates that the change in standard enthalpy is constant, which suggests that there is no significant change in retention mechanism over the temperature range of 20–45°C . The enthalpy of the chromatographic process can be calculated from the slope (), and the relative entropy can be determined from the intercept ().…”

“…Extensive studies on the shape selectivity of alkyl‐ and phenyl‐bonded stationary phases have been performed using polycyclic aromatic hydrocarbons (PAHs) . Sander and Wise found that the shape selectivity is controlled by the type of stationary phase, its bonding density, the length of the alkyl ligand, and the degree of ordering of the stationary phase.…”

Profiling Phospholipid Elution in Reversed-Phase Lc–MS/MS Bioanalytical Methods in Order to Avoid Matrix Effects

“…This apparent change in elution strength, as the concentration of MeCN in the mobile phase increases, also provides a likely explanation for the differing conclusions drawn in earlier reports with regard to whether MeOH or MeCN is the stronger eluting solvent [6,7]. The occurrence of U-shaped retention curves, from a general chromatography perspective, is believed to reflect a change in retention behavior from reversed phase (hydrophobic interactions between analyte and bonded organic phase, e.g., C18) to normal phase (ionic interactions between polar analyte and free silanol groups on the silica support) as the percentage of organic in the mobile phase increases (see for example [15] GPCs and free silanol groups, and subsequently reduce interactions between the two, MeCN is unable to shield such ionic interactions (see for example [16]). Therefore, as its concentration in the mobile phase increases, a normal-phase retention mechanism predominates.…”

New Advances in Separation Science for Metabolomics: Resolving Chemical Diversity in a Post-Genomic Era

“…192 However, bridged ethylene hybrid (BEH) modified silica stationary phases reduce the number of residual silanol moieties that contribute to undesirable ion-exchange processes while also improving the pH/thermal stability of the column. 193 The recent development of "superficially porous" sub-3 μm fusedcore particles provide highly efficient columns without high back pressures that achieve similar separation performance of sub-2 μm porous particles with standard HPLC instrumentation. 194 In this case, a 1.7 μm solid silica particle is used as support for growing an outer thin porous shell (0.5 μm) resulting in greater mass transfer kinetics even at high linear flow velocities.…”

“…Operating columns at elevated temperatures (>40 °C) offers a simple way for achieving faster separations at lower back pressures because of the lower viscosity of the mobile phase that can enhance peak capacity up to 1000 with plate numbers in excess of 100 000. − Nevertheless, most siloxane-based materials have limited pH stability (pH ≈ 6–8) at high temperatures, whereas residual silanol residues can adsorb basic solutes resulting in band broadening and peak asymmetry . However, bridged ethylene hybrid (BEH) modified silica stationary phases reduce the number of residual silanol moieties that contribute to undesirable ion-exchange processes while also improving the pH/thermal stability of the column . The recent development of “superficially porous” sub-3 μm fused-core particles provide highly efficient columns without high back pressures that achieve similar separation performance of sub-2 μm porous particles with standard HPLC instrumentation .…”