Evaluation of the elution strength of the surfactant and organic solvent in hybrid micellar mobile phases

The global ability of a mixed mobile phase (with two or more modifiers) to elute a solute is often measured without distinguishing between the elution strength of each modifier. An algorithm is proposed to evaluate the elutio n strength of the modifiers in hybrid micellar mobile phases containing a s urfactant and an organic solvent. The algorithm is based on a mechanistic r etention model that takes into account the competing equilibria of solutes among aqueous-organic phase, micelle, and stationary phase. The change in t he elution strength of surfactant and organic solvent with respect to the c oncentration of both modifiers is also examined. The results are discussed according to the values of the partition constant s of the solutes, and show the complex behaviour of the elution strength in the hybrid mobile phases, which depends on the relative concentration of t he different modifiers. The elution strengths of the surfactant sodium dode cyl sulphate and three alcohols, 1-propanol, 1-butanol, and 1-pentanol, are studied, using the retention data of six probe compounds (acebutolol, amil oride, carteolol, orciprenaline, triamterene, and trimethoprim).