Chromatographic retention, proposed mechanism

In this work correlations between mobile phase solvent strength and chromatographic retention of a number of different solute families will be presented. The first solvent strength measurements on ternary mobile phases will also be presented. Finally, a retention mechanism for packed column SFC is proposed. 

Several different physicochemical models have been proposed to predict and explain the retention behavior in liquid-solid chromatography. The models can be divided into two groups depending on the assumptions made concerning the fundamental mechanism of the chromatographic process. The two assumptions are as follows ... 

In the past, several theoretical models were proposed for the description of the reversed-phase retention process. Some theories based on the detailed consideration of the analyte retention mechanism give a realistic physicochemical description of the chromatographic system, but are practically inapplicable for routine computer-assisted optimization or prediction due to then-complexity [9,10]. Others allow retention optimization and prediction within a narrow range of conditions and require extensive experimental data for the retention of model compounds at specified conditions [11]. 

Modeling and Optimization. Fundamental studies increased the knowledge of the micellar retention mechanisms It was then possible to propose theoretical models that allowed chromatographers to predict and optimize their MLC separations [48-50]. 

Hydrophobicity is repulsion between a nonpolar compoimd and a polar environment, such as water. The distribution and hydrophobicity of hydrophobic amino acids are characteristic of each protein, so a specific separation is possible with use of hydrophobic supports. Different models are used for the description of protein hydrophobicity and hydrophobic interactions, and different theories are proposed for the retention mechanism of proteins in HIC [31]. In addition to the important role of water in the strengthening—weakening of the hydrophobicity, these interactions can be induced by changing the ionic strength, presence of organic solvents, temperature, and the pH value of the chromatographic media. Based on these properties, the HIC separation occurs by the modulation of the frequency and distribution of surface-exposed hydrophobic amino-acid residues, the hydrophobicity of the medium, the nature and composition of the sample, as well as type and concentration of salt in the mobile phase (see Figure 7.6). 

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