Study of chemical selectivity of molecular binary mixed micelles of sodium 10-undecenyl sulfate and sodium N-undecenyl leucinate using linear solvation energy relationships model

Poly(sodium 10-undecenyl sulfate) (poly-SUS), poly(sodium N-undecenyl leucinate) (poly-SUL) and their five molecular binary mixed micelles with varied SUS:SUL composition were prepared and used as pseudostationary phases in micellar electrokinetic chromatography (MEKC). Linear solvation energy relationships (LSERs) model and free energy of transfer studies were used to characterize the retention behavior and the selectivity differences among the seven surfactant systems. System constant differences and regression models for varied benzene derivative compounds are used to establish the selectivity differences of the seven pseudostationary phases. The cavity formation and dispersion interaction (the v system constant) and the hydrogen-bonding acidity (the b system constant) of the surfactant systems were found to have the most significant influence on selectivity and MEKC retention. The molecular micelle with sulfate head group, poly-SUS, was found to be more hydrogen-bond acidic than the molecular micelle with leucinate head group, poly-SUL. The other system constants (a, s and e) have modest effect on the retention and selectivity of the benzene derivatives. The model intercept coefficients (c system constants), which are negative for all surfactant systems have unusually large values. The free energy changes of transfer for the functional groups studied have all negative values except phenol and benzyl alcohol. Selectivity differences between pseudostationary phases were also compared by plotting the log k values against each other and were found to agree well with LSER results.