Bonded phase predicting retention behavior

This equation predicts a linear relationship between the logarithm of the retention factor and the molal salt concentration, which is indeed commonly observed. Figure 13.1 shows the retortion behavior of several proteins on a silica-based polar bonded phase, propylacetamide. The eluents were various concentrations of ammonium sulfate in 0.1 M phosphate buffer, pH 7. The slope of the relationship is 2-2.S (LAnoI) for this stationary phase. For n-butyl-and phenyl-derivatized silica-based phases, values of between 1 and 2 (LAnoO were observed (5). 

As pointed out by Mirrless et al. 78), a major limitation of the HPLC technique as compared to the shaking-flask method has to do with the behavior of sparingly soluble compounds (high A ow) which tend to give anomalously low log A ow values. This phenomenon results presumably from a slow equilibration of these compounds in the colunm phases so that a true equilibrium is not reached at elution breakthrough. To overcome part of this difficulty, Veith et al. 104) used a solvent mixture of water/methanol (15/85, v/v) as the mobile phase with octadecylsilane as the stationary phase, which was permanently bonded to a support (LiChrosorb). They found a reasonably good linear relationship between log RT (retention time) and log K over 6 orders of magnitude in K. This technique does not involve tedious column preparation and the column has better stability. With proper choice of standard compounds, the accuracy of the predicted log K values was estimated to be within 22.8 20.0%. 

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