Chromatographic retention factor

In addition to the above strategies, the use of higher column temperatures is another approach that may decrease analysis time and improve sample throughput. The relationship between the chromatographic retention factor, k, and separation temperature is shown in Equation 13.1 ... 

The chromatographic retention factor, k, is related to the equilibrium constant for adsorption to a solid phase or distribution between liquid mobile and stationary phases by the well-known expression... 

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 separation of uncharged compounds in CEC occurs as in HPLC due to their partitioning between the stationary and the mobile phases, with the only difference that the movement of the mobile phase through the column is propelled by electroosmosis in CEC and by a mechanic pump in HPLC. Consequently, the retention of uncharged analytes can be described by the chromatographic retention factor, k, which is expressed by the well-known equation ... 

The value of the second virial coefficient A 2 can also be determined from the retention volume that is obtained from self-interaction chromatography (Aliamed et al., 2005 Winzor et al., 2007 Dumetz et al., 2008). The chromatographic retention factor k is calculated from the retention volume VT using the formula... 

Case 1. The electrophoretic mobilities and the corresponding M-factors of the two components are identical. Since their chromatographic retention factors and thus their M/c are different, their MCec,packed will also be different so that X and Y are separable by CEC, e.g., components A and B are both neutral, differing only in their chromatographic retention factors and comigrating when X = 0 as illustrated in Fig. 1.12. The separation of A and B improves with increasing X and optimum separation is achieved when X is 0.9, i.e., the detection window is located immediately after the retaining frit as in conventional CEC columns. 

Case 2. The chromatographic retention factors and the M/c of X and Y in this case are identical. Since their electrophoretic mobilities and MCe are different, there MCec will be different too and the two components can be separated in CEC, e.g., components B and C have the same chromatographic retention factors, but different electrophoretic mobilities. Hence, they are separated by virtue of differential electrophoretic migration as illustrated in Fig. 1.12. 

Case 3. X has a smaller chromatographic retention factor and a higher electrophoretic mobility in the EOF direction than Y. So M/Cix> Micj and MCe,X> Mcejiti the two segments. Thus, MCec,X> MCec,Yin both the segments so that chromatographic and the electrophoretic forces act in concert to facilitate the separation of X and Y... 

For retained analytes with a chromatographic retention factor k the linear flow velocity ux is ... 

However, there are obvious differences between the classically determined octanol-water partition data and the reversed phase chromatographic partition data due to the different nature of the partitioning solvents. The correlation between shake flask octanol water partition coefficients and chromatographic retention factor kw (0 % organic solvent) was described to be low (Valko 2004) when structurally diverse compound sets were analysed. Using the q>o or the CHI lipophilicity index an improvement in agreement to logPow was reported (Valko 1993,1997). 

The k" measures the magnitude of retention in CEC due to reversible binding of the analyte to the stationary phase. Inspection of Eq. (11) shows that for all components (neutral or charged), k" is always positive, as a chromatographic retention factor should be. Further, while the retention factor in HPLC and the velocity factor in CZE are able to characterize the respective differential migration processes alone, both of them are required to characterize CEC. 

Association of the chromatographic retention factor with the equilibrium constant is the basis for all optimization or prediction algorithms. As was shown in Chapter 2, this association is only very approximate and should be used with caution. 

The earliest application of the Tucker3 model in chemistry is from the work of Spanjer [1984] and de Ligny et al. [1984] working with chromatographic applications. In this application two three-way data sets are analyzed. The first data set contains measured normal-phase liquid chromatographic retention factors of 19 solutes, measured on six different stationary phases at two mobile-phase compositions. This results inal9x6x2 array. The solutes were monosubstituted benzenes and polycyclic aromatic compounds. The second data set is a 39 x 3 x 2 array. It contains retention values of 39 more complicated solutes, viz.,... 

To be correct the terms in the brackets should be activities and not concentrations, also, two of the terms involve stationary phase activities that cannot be easily evaluated. The weight distribution coefficient for the sample ion A is given by Da = [As ] / [Am ] and is related to the chromatographic retention factor for the sample ion by Ra = Daw / Vm, where w is the weight of stationary phase and Vm is the column hold-up volume. Substituting these terms into Eq. (4.22) after rearrangement, we have... 

The apparent electrophoretic mobility of an analyte in micellar electrokinetic chromatography depends on three factors the electroosmotic mobility for the system the fraction of analyte in the electrolyte solution and its electrophoretic mobility and the fraction of analyte in the pseudostationary phase, and the electrophoretic mobility of the micelles (assuming that the mobility of the analyte-micelle complex is the same as the micelle). If we introduce the chromatographic retention factor, defined as the ratio of the number of analyte molecules in the pseudostationary phase to the number in the... 

An apparent retention factor in capillary electrochromatography can be defined in the usual way as kcEC = (Ir - teo) / teo. In this case, the retention factor only retains the same physical interpretation as the chromatographic retention factor (section 1.4) for neutral... 

The hydrophobic nature of sugars is clearly reflected in their cosolvent effects on the aqueous solubilities of various hydrocarbons. Additional confirmative evidence is provided by the chromatographic affinity of sugars for polystyrene gel (Bio-Beads SM-4, Bio-Rad Labs., Richmond, CA. U.S.A.). The use of the chromatographic retention factor (k) (see eqn. 20) obtained with a nonpolar stationary phase as a measure of solute hydrophobicity is both theoretically and experimentally well founded (ref. 23,62-64). 

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