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Reversed-Phase and Hydrophobic Interaction Chromatography of Peptides and Proteins
Published in Juan A. Asenjo, Separation Processes in Biotechnology, 2020
Ziad El Rassi, Ann L. Lee, Csaba Horváth
In both RPC and HIC, the energetics of retention are conveniently treated by a thermodynamic model (Horváth et al., 1976, 1977; Molnâr and Horváth, 1977, 1980a,b; Horváth and Melander, 1977) that has adapted the solvophobic theory of Sinanoğlu (1967). The measure of chromatographic retention is the retention factor, k’, which is obtained directly from the chromatogram according to the relationship k'=tR−t0t0 where is the retention time of the eluite under investigation, and t0 is the mobile-phase hold-up time in the column. The reversible binding of an eluite to the stationary-phase ligates is characterized by the equilibrium constant, K, which is related to the retention factor and given by the expression k'=ϕK where ϕ is the phase ratio.
Mobile Phase Effects in Reversed-Phase and Hydrophilic Interaction Liquid Chromatography
Published in Nelu Grinberg, Peter W. Carr, Advances in Chromatography Volume 57, 2020
tm and Vm are also known as the column hold-up time and hold-up volume, respectively. The terms t0, and V0 are sometimes used instead of tm and Vm. tm (t0) is equal to the ratio of the column length, L, and the linear velocity of the mobile phase along the column, u. F is the flow rate of the mobile phase, a simple conversion factor between the retention times and retention volumes. The retention factor, k, depends on the nature of the solute, on the character of the stationary and the mobile phases, and on temperature, but is independent of the flow rate of the mobile phase, the dimensions of the column (provided that the density of packing is uniform, i.e., a constant phase ratio along the column). Hence, k is a fundamental parameter in the method development and optimization of HPLC separations. Theoretically, k is suitable for measuring thermodynamic quantities by chromatography, such as the Gibbs free energy, enthalpy or entropy. Unfortunately, the retention factors determined from the experimental retention data – Equation (1.2) – do not provide reliable information on the presumed mechanism of retention, as several different mechanisms may contribute to the actual k.
Fullerenes and Polycyclic Aromatic Hydrocarbons in Separation Science
Published in Paweł K. Zarzycki, Pure and Functionalized Carbon Based Nanomaterials, 2020
Yoshihiro Saito, Koki Nakagami, Ohjiro Sumiya, Ikuo Ueta
Thermodynamic behaviors during the retention of analytes have been well investigated in LC, and in general, a correlation between the logarithmic retention factor and the reciprocal column temperature, which is widely recognized as the van’t Hoff plot, has been obtained in the temperature range normally employed in LC separations. In the general thermodynamic trend, the retention factor will decrease by increasing the column temperature. If a linear van’t Hoff plot is obtained in a range of column temperature, it is normally suggested that the retention mechanism remains the same in the temperature range, where the enthalpy of solute transfer from the mobile phase to the stationary phase can be estimated from the slope of the linear van’t Hoff plot. From the retention behavior of PAHs on the liquid-crystal phase at different column temperatures, the phase has an excellent molecular shape recognition capability even at a high column temperature, although the molecular shape recognition power is gradually decreased with increasing the column temperature. The obtained van’t Hoff plots for typical PAHs could be regarded as a linear relationship, and therefore, the retention mechanism in the temperature range was kept constant. The above trend has quite a good agreement with the selectivity study for ODS phases at various column temperatures: a good molecular shape selectivity can be obtained at a low column temperature, while the recognition ability will be decreased by increasing the temperature. That means that the fundamental trend on the shape selectivity of the liquid-crystal bonded phase is regarded as similar to that on typical ODS phases, although a better shape recognition power to a certain pair of PAHs can be observed on the liquid-crystal bonded phase due to the rigid ligand structure.
Identification of sugars as root exudates of the macrophyte species Juncus effusus and Philodendron cordatum in constructed wetland-microbial fuel cells during bioelectricity production
Published in Environmental Technology, 2022
Oscar Guadarrama-Pérez, Gabriela Eleonora Moeller-Chávez, Victoria Bustos-Terrones, Rosa Angélica Guillén-Garcés, Jesús Hernández-Romano, Martín Barragán-Trinidad, Edson Baltazar Estrada-Arriaga, Victor Hugo Guadarrama-Pérez
The relationship between the distances traveled by the solute and the eluant from the origin of the TLC plate (mobile phase) is known as the retention factor (Rf). This value remains constant for each specific compound under certain adsorption chromatographic conditions. The concept of Rf expresses the position of a compound on a plate (stationary phase) as a decimal fraction that measures the retention distance of a component. Since it is extremely difficult to reproduce the experimental conditions exactly, the comparison of one sample with another must be done by eluting both plates simultaneously. The results of this parameter are used as references for future tests. To calculate the Rf value, the following expression was applied: Rf = distance traveled by the identified compound (X)/distance traveled by the eluent (Y) and the values obtained are shown in Table 2.
Diclofenac removal in water supply by adsorption on composite low-cost material
Published in Environmental Technology, 2021
Gledson Renan Salomão, Juliana Heloisa Pinê Américo-Pinheiro, William Deodato Isique, Nádia Hortense Torres, Ianny Andrade Cruz, Luiz Fernando Romanholo Ferreira
Retention factor (k) is usually the first chromatographic parameter to be adjusted, not too small (demonstrates that the compound interacts little with the stationary phase), or too large (causes band widening). Being k very small means that the mobile phase is very strong and/or solute has little interaction with the stationary phase, while a very large k implies that the mobile phase is very weak and/or the solute has a lot of affinity with the stationary phase. Therefore, it is important to emphasize that, in separations of complex mixtures by the isocratic mode, rarely ideal values of k will be obtained for all components of the sample, so the use of gradient elution is recommended [35].