RELIABILITY OF THE CAPACITY FACTOR AT ZERO MICELLAR CONCENTRATION ANDTHE SOLUTE-MICELLE ASSOCIATION CONSTANT ESTIMATES BY MICELLAR LIQUID-CHROMATOGRAPHY

In micellar liquid chromatography, MLC, the hydrophobicity of a compou nd is the predominant effect on its retention and interaction with mic elles. The capacity factors at zero micellar concentration, k(m), and the solute-micelle association constants, K-AM, have recently been use d as the hydrophobicity index of compounds and are important in QSAR s tudies. These parameters could be estimated (by regression) from the ( k,[M]) data, where k is the capacity factor and [M] the surfactant con centration minus the critical micelle concentration. k(m) and K-AM are usually obtained from the intercept and slope, respectively, of the p lot 1/k vs, [M]. In spite of the general use of this equation, the rel iability of the estimates has not received special attention. Two new regression models have been proposed: a nonlinear model (plot k vs. [M ]) and a new linear model (k vs. k . [M]). The reliability of the k(m) and K-AM estimates is studied with the aid of simulated data, and the conclusions obtained from the theoretical study are contrasted with e xperimental data, The influence of variables like the hydrophobicity o f compounds, K-AM/k(m) ratio, the uncertainty of experimental k data a nd the experimental design have been considered, Some critical aspects of the models and recommendations for their use are provided. (C) 199 7 Elsevier Science B.V.