Variation of the Eluent Conditions

The third column in Table 3 reflects the increase in the C-parameter when switching from pH 2.8 to 7.0, thus increasing the ion-exchange capacity of the stationary phase. The two non-endcapped Zorbax phases SB-100 and SB-90 show an extraordinary behavior, which must be related to a greater presence of acidic silanol groups. 

Provided that the effects on the C-parameter can be neglected, it can be concluded that a meaningful phase characterization using the empirical LFER approach can be carried out under one single set of eluent conditions. 

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In the first publication [16], the experimental strategy was applied to just ten different stationary phases, in part different modifications of the same silica-based material. Phases with incorporated polar fimctions were not included. The eluent conditions were kept constant. The chromatographic experiments with all of the neutral substances were carried out with a H2O/CH3CN (1 1, vjv) eluent with buffer additives, while basic and acidic solutes were eluted with a 31.2 mM phosphate buffer at pH 2.8. The selected pH value does not imply very critical conditions, as it suppresses dissociation of most residual silanol groups and of weakly acidic solutes. A variation of the eluent conditions wiU be discussed in a later section. 

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