Mobile phase effects

Unfortunately, none of the commonly used molecular probes is adequate to evaluate column-to-column variabilities [88]. The absolute prediction of retention of any compound involves the use of a rather complex equation [89,90] that necessitates the knowledge of various parameters for both the solute and the solvent [91]. The relative prediction of retention is based on the existence of a calibration line describing the linearity between log and interaction index. This second approach, although less general than the first, is simpler to use in practice, and it often gives more accurate results than the first. With a proper choice of calibration solutes, it is possible to take into account subtle mobile phase effects that cannot be included in the theoretical treatment. 

P.H.J. Schoeiunakers, A Systematic Approach to Mobile Phase Effects in RP-HPLC, thesis. Delft 1981. 

Sun, Y. and Stalcup, A. M., Mobile phase effects on retention on a new butylimidazolium-based high-performance liquid chromatographic stationary phase, /. Chromatogr. A, 1126,276-282, 2006. 

Chang, C.A., Wu, Q., and Eastman, M.R, Mobile phase effects on the separations of substituted anilines with a-cyclodextrin-bonded column, J. Chromatogr., 371, 269, 1986. 

Equation 12.26 is indeed remarkable in that, as far as the mobile phase is concerned, h is a function only of v and the packing-structure constants y, A, and packed columns with similar packing constants, the h versus v curves representing mobile phase effects will be about the same. This will be true in comparing GC and LC columns as well, despite the fact that diffusivity Dm typically differs by 104 between gases and liquids and dp varies by a factor of ten or so. 

Perkin Trans. 2, 2087 (1988). Solute-Sovent Interactions in Chemistry and Biology. Part 7. An Analysis of Mobile Phase Effects in High Pressure Liquid Chromatography Capacity Factors and Relationships of the Latter with Octanol-Water Partition Coefficients. 

E. Mobile-Phase Effects Involving Organic Solvent... 

Several fundamental models have recently been proposed (//, I7a,b, 28) in order to quantitatively accommodate the influence of solution equilibria on the distribution process. Although application of these theoretical approaches has yet to provide a comprehensive general description of retention behavior for peptides, they have provided useful insight into those mobile-phase effects arising from changes in the nature and mole fraction of the organic solvent modifier. 

MOBILE-PHASE EFFECTS IN LIQUID-SOLID CHROMATOGRAPHY... 

A m or challenge to completing a practical model and description of mobile-phase effects in LSC is the further elucidation of hydrogenbonding effects. This will involve a more fundamental classification of solutes and solvents in terms of their proton-donor and proton-acceptor properties, so that values of can be estimated as a function of the molecular structures of solute X and solvent C. It will also require a more precise description of the adsorbate-surface bonding that occurs in the adsorbed monolayer, so that values of can likewise be rationalized and predicted. 

The various aspects of displacement and localization are now well understood, and predictions of their effects on retention in LSC can be made with some confidence. Hydrogen bonding between solute and solvent molecules requires further investigation, and it is likely that such studies will contribute to our understanding of hydrogen bonding in solution as well. On the basis of the present model it should prove possible to systematically explore new stationary phase compositions for unique separation potential. However, this subject falls outside the area of mobile-phase effects per se, and will be reserved for another time. 

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