Comparison of micellar isotherms of benzene determined by headspace gas chromatography and micellar electrokinetic chromatography. Assessment on impact of buffer and solubilization-induced conductivity change.
The possibility is discussed that micellar isotherms determined by vacancy-micellar electrokinetic chromatography (vacancy-MEKC) differ from isotherms in electrolyte-free surfactants due to thermodynamic effects of buffer. Also discussed is the possibility that they are biased at high solute concentrations by solubilization-induced changes of electrical conductivity. Such bias could invalidate a theory on peak asymmetry of neutral solutes in MEKC that is based on thermodynamic interpretation of the isotherms. To evaluate these possibilities, the nonlinear concave upward isotherm of benzene in a pH 7.0, 0.0060 M sodium phosphate buffer containing 50 mM sodium dodecyl sulfate (SDS) was measured by headspace gas chromatography. Of interest is the finding that benzene is more stable in the surfactant-free buffer than in water. The isotherm was compared to that previously measured by vacancy-MEKC in the same buffer and 10, 30, or 50 mM SDS. No difference was found between the isotherms. However, the isotherm indeed differed from that of benzene in buffer-free 50 mM SDS, which was also determined and agreed favorably with previous results. A partial explanation is given for the independence of the vacancy-MEKC isotherm of solubilization-induced conductivity changes.
Liu
Siyuan
S
Department of Chemistry and Biochemistry, Southern Illinois University at Carbondale, Carbondale, IL 62901, USA.
Davis
Joe M
JM
D001554:Benzene / Q000032:analysis; D002021:Buffers; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002849:Chromatography, Gas / Q000379:methods*; D020374:Chromatography, Micellar Electrokinetic Capillary / Q000379:methods*; D004553:Electric Conductivity; D006863:Hydrogen-Ion Concentration; D008823:Micelles; D008956:Models, Chemical; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D012995:Solubility; D013816:Thermodynamics
D002021:Buffers; D008823:Micelles; D012967:Sodium Dodecyl Sulfate; D001554:Benzene