Selectivity and elution strength

Elution Strength and Selectivity with Micellar Systems... 

V. EFFECT OF ORGANIC MODIFIERS ON THE ELUTION STRENGTH AND SELECTIVITY... 

In aqueous-organic systems, it is common practice to first adjust the elution strength, and then optimize the selectivity at a constant elution strength. In hybrid systems, where an increase in elution strength can often coincide with an enhancement in selectivity, a separate optimization of elution strength and selectivity is inefficient. This is the main subject treated in Chapter 8, where it is shown how the simultaneous optimization of parameters influencing elution strength and selectivity can be performed. 

The elution strength and selectivity obtained with the o/w microemulsion mobile phases was acceptable. For example, the k factor of the apolar acebutolol and nadolol compounds (P adrenergic blockers) were 13.5 and 18.2, respectively, with a 100% methanol mobile phase (selectivity a = 1.5). The corresponding retention factors were 14 and 3 with Microemulsion 2 (a = 4.7) and 5.5 and 1.8, respectively, with Microemulsion 4 (a = 3.1) [4]. Chlorthalidone, a polar diuretic, was almost not retained with the 100% methanol mobile phase (k=0.37). With Microemulsions 3, 4 and 5, its retention factors were 1.04, 0.76 and 1.83, respectively. Figure 13.2 shows that it was possible to directly inject urine samples. Proteins and/or UV absorbing biological material produced an early eluting peak whose width was related to die microemulsion heptane content [4]. 

In MLC, the retention behavior (elution strength and selectivity) can be quite different from the observed... 

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