Monomeric and polymeric anionic gemini surfactants and mixed surfactant systems in micellar electrokinetic chromatography. Part I: characterization and application as novel pseudostationary phases.

Sodium di(undecenyl) tartarate monomer (SDUT), a vesicle-forming amphiphilic compound possessing two hydrophilic carboxylate head groups and two hydrophobic undecenyl chains gemini surfactant, was prepared and polymerized to form a polymeric gemini surfactant (i.e., poly-SDUT). These anionic surfactant systems with carboxylate (SDUT and poly-SDUT) and sulfate (sodium dodecyl sulfate, SDS) head groups as well as mixed surfactant systems (SDS/SDUT, SDS/poly-SDUT, and SDUT/poly-SDUT) were then applied as novel pseudostationary phases in micellar electrokinetic chromatography (MEKC). The SDUT and poly-SDUT were characterized using various analytical techniques. Retention factors of 36 benzene derivatives were calculated in 20 mM phosphate buffer of each surfactant system. The retention factor values of the test solutes show that there are distinctive selectivity differences between the surfactant systems. Solute-pseudostationary phase interactions in MEKC were also examined by determining the free energy of transfer of the substituted functional groups from the aqueous buffer phase into the pseudostationary phase.

Combination of cyclodextrins and polymeric surfactants for chiral separations.

A cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) method was applied to the enantioseparation of three binaphthyl derivatives using neutral CDs (i.e., beta- and gamma-CD) in combination with various chiral amino acid-based polymeric surfactants (PSs). Both the D- and L-configurations of poly(sodium N-undecanoyl alaninate), poly(sodium N-undecanoyl leucinate), and poly(sodium N-undecanoyl valinate) (poly(L-SUV)) were synthesized. The retention behavior of the three binaphthyl derivatives under optimum electrophoretic conditions using a single chiral additive (PS or CD) is discussed. In addition, the effect of CD cavity size and stereochemical configuration of polymeric surfactants on selectivity (alpha) and resolution (Rs) was investigated. The enantioseparation of (+/-)1,1'-binaphthyl-2,2'-diamine gave a reversal of enantiomeric order when using beta-CD in combination with any of the three D-configuration PS. However, better enantioseparation is obtained when using the corresponding L-configuration PS with beta-CD. A reversal of migration order (RMO) for the enantiomers of (+/-)1,1'-bi-2-naphthol was observed upon the addition of 10 mM gamma-CD to poly(L-SUV). However, no RMO of (+/-)1,1'-bi-2-naphthol was seen when either beta-CD or gamma-CD was combined with D-PS. The enantiomers of (+/-)1,1'-binaphthyl-2,2'-diyl hydrogen phosphate showed little enantioselective behavior toward the PS alone. However, combined D- or L-PS and beta-CD or gamma-CD systems gave increased Rs and alpha values. The chiral recognition of binaphthyl derivatives observed resulting from the various combinations of two chiral selectors is discussed.