Retention behavior of solutes

The retention behavior of solutes in adsorption" chromatography can be described either by the "competition" model or by the "solute-solvent interaction" model depending on the eluent composition. It appears that both mechanisms are operative but their importance depends on the composition of the eluent mixture 84). 

The problem with using surfactant-modified stationary phases in LC is that the surfactant will usually slowly elute (bleed) from the support thus resulting in different retention behavior of solutes with time. This is why most applications are in the area of GC or GLC. An exciting recent advance has been reported by Okahata, et al (181). Namely, a procedure has been developed for immobilizing a stable surfactant vesicle bilayer as the stationary phase in GC. A bilayer polyion complex composed of DODAB vesicles and sodium poly(styrene sulfonate) was deposited on Uniport HP and its properties as a GC stationary phase evaluated. Unlike previous lipid bilayers which exhibited poor physical stability, the DODAB polyion phase was stable. Additionally, the temperature-retention behavior of test solutes exhibited a phase transition inflection point. The work demonstrates that immobilized surfactant vesicle bilayer stationary phases can be employed in GC separations (181). Further work in this direction will likely lead to many such unique gas chromatographic supports and novel separations. 

Zhang, Q.H. Feng, Y.Q. Yan, L. Da, S.L. Wang, Z.H. Retention behavior of solutes on liquid chromatographic column packed with dynamically modified zirconia. Chin. J. Chromatogr. 1999, 17, 229-231. 

Only one research group has illustrated the reversed phase retention behavior of solutes on zirconia-silica modified surfaces. In the study by Melo et al. on PMOS gamma-irradiated modified surfaces, the reversed phase retention behavior of a test mixture containing acetone, benzonitrile, benzene, toluene, and naphthalene was evaluated. The authors illustrated good resolution of the five-component text mixture as shown in Fig. 7. Retention, however, decreased after the stationary phase was washed with 5000 column volumes of base (pH 10). Despite the base washing, uniform peak shape was maintained, with only a slight reduction in resolution as discussed in Alkaline Stability above. 

J.R. Torres Lapasio, R.M. Villanueva Camanas, J.M. Sanchis Mallols, M.J. Medina Henmdez and M.C. Garcia Alvarez-Coque, Modeling of the Retention Behavior of Solutes in MLC with Organic Modifiers, J. Chromatogr., 639 87 (1993). 

The retention behavior of solutes will depend on the type of interactions with the micelles and with the surfactant-modified stationary phase. Nonpolar solutes should only be affectedby hydrophobic interactions (Fig. 5.1a). For these solutes, different proportions of nonpolar, dipole-dipole and proton donor-acceptor interactions between solutes and... 

A more complex approach in QSRR is the description of the retention behavior of solutes by a multiparameter equation that includes several descriptors related to different structural properties. Chromatographic retention data must be some function of the chemical structure of solutes, stationary phase and mobile phase, all of them mutually interacting. However, there is no general, strict, canonical nation relating the retention to these variables. Even if the stationary and mobile phases in a given chromatographic system remain constant, still a precise quantitative description of the retention of a series of solutes appears problematic, and the difficulties increase with the diversity of the solutes consider. The problem is also not trivial for homologues. 

In order to establish a scale of polarity, one needs a reliable method for specifying and measuring the retention behavior of solutes. Parameters such as retention volume and retention factor would seem to be suitable, but they are subject to too many variables. Relative values are much better, and one such parameter originally defined by Kovats [2] has been well received. It uses a homologous series of n-paraffins as standards against... 

Garcia-Alvarez-Coque, M.C. Torres-Lapasio, J.R. Baeza-Baeza, J.J. Modelling of retention behavior of solutes in micellar hquid chromatography. A review. J. Chromatogr. A, 1997, 780, 129-148. 

Retention behavior of solutes on liquid chromatographic column packed with dynamically modified zirconia. Chin. 

Only one research group has illustrated the RP retention behavior of solutes on zirconia-silica modified surfaces. In the study by Melo et al. on PMOS gamma-irradiated modified surfaces, the RP retention behavior of a test mixture containing acetone, benzonitrile, benzene, toluene, and naphthalene was evaluated. The authors... 

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