QUANTITATIVE RETENTION - STRUCTURE AND RETENTION - ACTIVITY-RELATIONSHIP-STUDIES OF IONIC AND NONIONIC CATECHOLAMINES BY MICELLAR LIQUID-CHROMATOGRAPHY

When ionic surfactants are used as mobile phases in micellar liquid ch romatography, MLC, the retention of compounds is governed by hydrophob ic and electrostatic forces. In the absence of electrostatic effects, the hydrophobicity of a compound is the predominant factor affecting i ts retention and its interaction with micelles. Because both interacti ons should be considered for ionic compounds, a novel retention model is proposed which includes the hydrophobicity of a compound and the mo lar fraction of its charged form. High correlations between the logari thm of the capacity factors and structural parameters were obtained fo r ionic compounds with different degrees of ionization. The effect of the nature and composition of the mobile phase (pH, concentration of s urfactant and modifier) was studied. The modelling of the retention of compounds as a function of physico-chemical parameters and experiment al variables was established by means of multivariate regression metho ds (MLR, PLS). In addition, a predictive model for estimating the hydr ophobicity of catecholamines is proposed. Finally, quantitative retent ion activity relationships in MLC were also investigated for calechola mines.