Factors determining AO selection

Selectivity is more important than efficiency (AO in determining resolution because Rs is directly proportional to selectivity, but is proportional only to the square root of efficiency (see Fig. B4.2.5 along with Equation B4.2.1 and Equation B4.2.2. Hence, a four-fold increase in efficiency is required to double resolution, as compared with a two-fold increase in selectivity. In practice, selectivity depends partly on the chromatographic technique employed but can usually be controlled by manipulating experimental conditions, such as the pH and ionic strength of the mobile phase. Because this can be done easily and predictably, selectivity is the factor that is exploited to achieve maximum resolution in column chromatography rather than efficiency, which is fixed by the particle size and uniformity of the medium selected. 

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