Micellar phase capacity factor

In a given volume of the micellar solution of the solute species i, the micellar phase capacity factor (see definition (1.4.1), also called the distribution ratio) may be... 

Analogously to chromatography, the capacity factor kP can be defined as the ratio of the residence times of the analyte molecule in the mobile (aqueous) and stationary (micellar) phases (Nemstian distribution). The mathematical description is based on the assumption that attainment of the distribution equilibrium takes much less time than the duration of the migration of the solute. The components involved should not show any interaction with the capillary wall. As in almost all cases where UV detection is... 

For Eq. (2) it is assumed that the volume of the micellar phase is proportional to the tenside concentration and that the partial molar volume v remains constant. (See Chapter 2.) A further prerequisite for the application of Eq. (2) is a constant ionic mobility of the micellar phase independent of the uptake of a solute (/x, . = const.). In contrast to HPLC, substances that have an infinitely high kP value, i.e., that are completely dissolved in the micellar phase, can be detected. In this case the sample molecule migrates with the mobility of the micelle. In the presence of several different micellar phases (coexistence of simple and mixed micelles), the calculation of kP is possible only when partial capacity factors are known (20). The determination of kP is then considerably more complicated. 

To calculate the capacity factor, it is necessary to know the migration time not only of the analyte but also of the micelle and the EOF. Although there is no ideal marker in MECC, a very hydrophobic molecule, such as Sudan III, will spend most of its time partitioned in the micellar phase and... 

As with the capacity factor, as the velocity of the micellar phase approaches zero, the equation for resolution approaches that of classic chromatography. 

The separation on the ODS-SDS column is achieved by the addition of a suitable complexing ligand to the mobile phase to discriminate between the various metal ions. The selectivity between two metal ions is achieved through two competing equilibria, namely the complexation equilibrium of the free metal ion in the micellar pseudo-phase and the complexation equilibrium of the metal ion adsorbed on the SDS mono-layer and this is shown in Fig. 1. It is evident from this equilibrium that the distribution ratio (capacity factor) of the metal ion is given by Eq. (1), where the subscripts a and represent the concentration of the free metal ion in the bulk aqueous phase and the adsorbed monolayer, respectively ... 

Armstrong and Nome " have shown that chromatographic methods such as high-pressure liquid chromatography (HPLC) and thin layer chromatography (TLC) can be used for determination of partition coefficients. The aqueous micellar solutions are used as the mobile phase. When the concentration of micelles in the mobile phase is increased, the retention and capacity factors of... 

In conventional reversed phase HPLC, differences in the physicochemical interactions of the eluate with the mobile phase and the stationary phase determine their partition coefficients and, hence, their capacity factor, k. In reversed-phase systems containing cyclodextrins in the mobile phase, eluates may form complexes based not only on hydrophobicity but on size as well, making these systems more complex. If 1 1 stoichiometry is involved, the primary association equilibrium, generally recognized to be of considerable importance in micellar chromatography, can be applied (11-13). The formation constant, Kf, of the inclusion complex is defined as the ratio of the entrance and exit rate constants between the solute and the cyclodextrin. Addition of organic modifiers, such as methanol, into the cyclodextrin aqueous mobile phase should alter the kinetic and thermodynamic characteristics of the system. This would alter the Kf values by modifying the entrance and exit rate constants which determine the quality of the separation. 

A three-phase equilibrium model for partitioning of solute, E, between a bulk aqueous phase and dissolved cyclodextrin, and between the bulk aqueous phase and the stationary phase, L3, allows one to derive equations relating capacity factor, k, to the molar concentration of CD. The equation given below is similar to that derived for micellar chromatography which also assumes a three-phase model (12. 131,... 

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