Regular retention behavior

Micellar mobile phases of anionic, cationic, nonionic and zwitterionic surfactants are used in conjunction with different bonded stationary phases (including C8, Cl8 and cyano). Considerably less surfactant (usually <0.2 M) is used compared to the organic modifier content in an analogous traditional separation. A variation in the concentration of surfactant is translated into an increase in the concentration of micelles in the solution, whereas the number of monomers of surfactant remain constant. As a consequence, the characteristics of the stationary phase modified by the adsorption of surfactant are very stable, and usually, a regular retention behavior is observed as a function of the concentration of surfactant. 

Important progress has been made in the application of gradient elution retention data for a particular peptide or protein mixture to the selection of isocratic elution conditions and vice versa based on a variety of predictive algorithms [302,356-360]. Furthermore, in large-scale RPC or HIC separations it is feasible in circumstances of regular retention behavior and high mass recovery to apply data derived from small-scale or analytical experiments as normalized integrals of... 

A disadvantage of simple interpretive methods is that the model to which the retention data (or other data) are fit must be fairly accurate. In other words, an interpretive approach may fail if one or more sample components exhibits anomalous retention. Although rare in SFC, such retention behavior is observed occasionally and is difficult to predict intuitively. Note, however, that by anomalous retention we do not mean behavior that is merely unusual, e.g., retention that decreases smoothly with increasing density (at constant temperature). Retention that varies in a regular (continuous) manner, even if unusual, can usually be modeled with a high degree of accuracy (vide infra). 

Convergence or divergence in the linearity of the plots of retention time versus the logarithm of the number of residues, i.e. /c iex i versus In d, can be employed to characterize the regular ion-exchange behavior of polypeptides in terms of the role of polypeptide chain length... 

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