Retention factor parameters

Solute equilibrium parameters (X5,S for RPC and (Xz,Z for lEC Solute retention factor for initial mobile phase A ... 

In order to illustrate the critical process parameters of SMB process validation, we will consider the separation of the racemic drug as described in Process design. The study represents the effect of the influence of feed concentration, number of plates and retention factor on the second eluting enantiomer. The simulation of the process for different values of feed concentration is performed and the variations of the extract and raffinate purities are shown in Fig. 10.10. 

The graph in Fig. 10.12 shows that the purity decreases very quickly below acceptable levels as retention factor of the more retained enantiomer decreases. Flowever, with minor adjustment of the SMB internal flow rates, a variation of more than 10 % of the retention factor of the more retained enantiomer still meets required purity, productivity, and eluent consumption. Control of critical parameters such as retention factors can be made without modification of the feed and eluent flowrates. 

The different organic modifiers used to derive the most suitable mobile phases lead to different parameters namely isocratic logfe and extrapolated logkw. The extrapolation method has no reality in terms of chromatographic behavior of solutes. However, mainly by correlation with log Pod (Eqs. 2 and 3) several studies have demonstrated the interest of these extrapolated retention factors as predictors of the lipophilicity of solutes. 

The retention factors of neutral (k0) and ionized forms ft,) can be related by the parameter f ... 

The resolution can be improved by increasing the column plate number, N, and/ or the separation factor, a (a = the ratio of the retention factors of the two compounds). N is the physical parameter and a is the chemical parameter for the separation. Higher N and a values give a better separation. 

While retention time is used for peak identification, it is dependent on the flow rate, the column dimension, and other parameters. A more fundamental term that measures the degree of retention of the analyte is the capacity factor or retention factor (k ), calculated by normalizing the net retention time (% > retention time minus the void time) by the void time. The capacity factor measures how many times the analyte is retained relative to an unretained component. ... 

In the System Suitability section, different parameters are described which can be applied in order to check the behavior of the CE system. The choice of the appropriate parameters depends on the mode of CE used. The system suitability parameters include retention factor (k) (only for MEKC), apparent number of theoretical plates (N), symmetry factor (Af), resolution (Rs)> Rtea repeatability, migration time repeatability, and signal-to-noise ratio. Practical equations to calculate different system suitability parameters from the electropherograms are presented, which are also included in Table 3. 

Fio. 43. Retention factor fo leveral amino acida data conform to Eq. (92) as shown by the curvee drawn using parameters given by Kroeff and Pietrzyk. The eluites are L-phenylalanine (L-Phe) oL leucine (ot-Leu) OL>valine (OL-Val), and OL-alanine (OL-Ala). Date were taken with 0.04 M phosidwte buftr at 0.2 M ionic strength with NaCl. Reputed with permission from Kroeff and Pietrzyk (208). Anal. Chem. Copyri t 1978 by the American Chemical Society. 

There is experimental evidence that dnder certain conditions RPC may possibly be used as an alternative method to evaluate a parameter equivalent to log P. Linear-relationships between logarithm of the retention factor and carbon number are anticipated in this optic and have been ob-... 

Debye-HOckel screening parameter, Eq. (43) common logarithm of the retention factor... 

The parameters obtained by analyzing experimental data iii view of Eq. (93) can be combined to calculate the so-called retention modulus (7/6), 7), which in our case is given by the ratio of the maximum retention factor at saturating hetaeron concentration to the retention factor measured with an otherwise identical chromatographic system in the absence of hetaeron as... 

In pHPLC, there are numerous types of columns used. The comparison and characterization of these columns are often discussed in terms of thermodynamic properties and kinetic characteristics. The retention factor, k, selectivity, a, and the peak asymmetry are believed to be representative parameters for the thermodynamic properties, while the kinetic characteristics are often expressed in dimensionless magnitudes of reduced plate height, h, separation impedance, E, and flow resistance factor, ( ). 3... 

The relative retention a=k/ki is a measure of the separation selectivity for two compounds i and j with retention factors ki and kj, respectively, differing by one repeat structural unit, An=l.p in Equation 5.16 is the end-group contribution to the retention factor. The conventional theory describes adequately the retention of oligomers and lower homopolymers and copolymers up to the molar masses 10,000-30,000Da for higher polymers the accuracy of the determination of retention model parameters is too low [95]. 

The ratio of the two virtual lengths defines a parameter called the electrophoretic velocity factor k, which is analogous to the chromatographic retention factor and it is expressed as [140] ... 

The migration behavior of neutral analytes in MEKC can be described by parameters similar to those employed in liquid chromatography [209], Hence, the ratio of the number of moles of the analyte in the micellar phase, the pseudostationary phase, (ttp p) to those in the surrounding solution (nip) defines the retention factor t... 

As evidenced by the above equation, the distribution coefficient can be directly calculated from the retention factor and other easily measurable parameters. It is also worth noting that when the concentration of the micellar phase is sufficiently low, the denominator at the last term of the above equation can be approximated to be equal to unity and the retention factor is linearly proportional to the concentration of the surfactant into the BGE. Accordingly, Equation 6.46 is rewritten as... 

Which parameters contribute an effect to the widths of the peaks on a chromatogram Is it true that all of the compounds present in a sample and which can be identified upon the chromatogram have spent the same amount of time in the mobile phase of the column Can it be said that a reduction in the retention factor k of a compound enhances its elution from the column ... 

---