Thermodynamics of Micelle−Water Partitioning in Micellar Electrokinetic Chromatography:  Comparisons with 1-Octanol−Water Partitioning and Biopartitioning

• Published in: Environmental science & technology 1997-10, Vol.31 (10), p.2812-2820
• Main Authors: Woodrow, Brian N, Dorsey, John G
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biochemistry; Biological and medical sciences; Chromatography; Ecotoxicology, biological effects of pollution; Environment; Fundamental and applied biological sciences. Psychology; General aspects; Ions; natural resources; Thermodynamics; Water; water management; water resources
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es9700313

Micellar electrokinetic chromatography (MEKC) was evalu ated as a model for biopartitioning. The thermodynamics for water−micelle partitioning are measured and compared with literature values for both biopartitioning and water−1-octanol partitioning. It was found that the free energy of transfer (ΔG) is dominated by the entropic term (ΔS) for both water−micelle partitioning and biopartitioning, but the enthalpic term (ΔH) dominates for water−1-octanol partitioning. Thermodynamic values of transfer and water−micelle partition coefficients are presented for a series of 67 solutes with varying functionalities. This work demonstrates the usefulness of MEKC for estimating biopartitioning by establishing a correlation between biopartitioning and water−micelle partitioning. Also, this method incorporates the economic advantages of capillary electrophoresis (CE), which include fast analysis times, low sample consumption, the use of aqueous buffer systems, and low organic solvent use and disposal. Solute retention for the MEKC buffer system used was evaluated through the use of enthalpy−entropy compensation plots. It was found that the mechanism of retention varied for each of four general solute classes:  strong hydrogen bonding solutes, single ring weak hydrogen bonding solutes, multiple ring weak hydrogen bonding solutes, and multifunctional hydrogen bonding solutes.