EFFECT OF MOLECULAR-STRUCTURE ON THE SOLUTE-MICELLE AND SOLUTE-STATIONARY PHASE BINDING CONSTANTS IN MICELLAR LIQUID-CHROMATOGRAPHY

The effects of molecular structure on the solute-micelle and solute-st ationary phase binding constants in micellar liquid chromatography (ML C) have been investigated. The following points have been observed. (1 ) There is quite a good linear relationship between the solute-micelle and solute-stationary phase binding constants in MLC with the cationi c (CTAB) and anionic surfactants as the additives, which means that th e contribution of physico-chemical properties of solutes on the solute -micelle and solute-stationary phase binding constants acts in a paral lel way. (2) Good quantitative relationships between the solute-micell e and solute-stationary phase binding constants and the solvatochromic parameters have been obtained, which indicates that the distribution mechanism of the neutral solutes in MLC is determined via their molecu lar interactions. Both the cavity process and the hydrogen bond intera ction play a very important role in the retention of neutral solutes i n MLC. The contribution of the hydrogen bond interaction, especially t he hydrogen donor ability of the solutes on those binding constants in anionic and cationic surfactant MLC, is determined in a different way . (3) Linear regression analysis of the solute-micelle and solute-stat ionary phase binding constants between the cationic and anionic surfac tant MLC has been carried out. The obtained results suggest that the t ransfer of the non-polar solutes from the aqueous phase to the anionic and cationic surfactant micelles acts in a parallel way, but that of the polar solutes in a different way. A model of micelles with three d ifferent sites of solubilization, i.e., (1) the core of the micelle, ( 2) the surface of the micelle and (3) the palisade layer of the micell e, has been used to successfully explain the observed results. Finally , the retention behavior of solutes in MLC is compared with that in re versed-phase liquid chromatography (RP-LC). It has been observed that there is no difference in separation selectivity for the non-polar sol utes between MLC and RP-LC; however, for the polar solutes, MLC provid es a different separation selectivity compared to that in RP-LC.