Copolymerized Micelles as Pseuodophases in Micellar Electrokinetic Chromatography

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The use of CE for analytical separations has many advantages over the other two commonly used chromatographic techniques, that is, gas chromatography and liquid chromatography. Some of these advantages include lower operating costs, much higher separation efficiency, small sample size required, short analysis time, versatility, and simplicity. Micellar electrokinetic chromatography (MEKC) was introduced in 1984 and is the CE mode most commonly used for enantiomeric separation. While MEKC is a very useful technique, it has several disadvantages. One disadvantage is that in order for the surfactant to be effective as a pseudostationary phase, it must be at a concentration above its CMC. In addition, the dynamic equilibrium between the free surfactant molecules and the micelle can lead to a decrease in separation efficiency as compared to a more ordered micellar system. To overcome these drawbacks, polymeric surfactants (or molecular micelles) were introduced. First advantage of molecular micelles is the elimination of the dynamic equilibrium between monomer and the micelle. Second advantage is the lack of a CMC, thus they may be used at concentrations well below the CMC of the unpolymerized surfactants. Single amino acid-based polymeric surfactants as chiral selectors for MEKC were first introduced in 1994. A major advantage of this approach is that different functionalities, such as a variety of chiral head groups (e.g., amino acids), can be integrated into the polymeric surfactants. This introduces an effective way of manipulating selectivity of the pseudostationary phase. In addition, the availability of both D and L optical configurations of amino acid-based pseudostationary phases is particularly advantageous to more accurately determine enantiomeric impurities by reversal of the migration order of the two enantiomers. The main disadvantage of these types of molecular micelles is that they are not soluble below pH 7.0 due to carboxylated head groups (e.g., amino acids). The PI intends to develop a new class of amino acid based polymeric surfactants that could be used at wider pH ranges. Highly soluble sulfated achiral surfactants and amino acid basid chiral surfactants will be copolymerized at various molar ratios to form novel copolymerized molecular micelles. These surfactants will be characterized using a variety of analytical methods and will be applied as pseudostationary phases in MEKC for separation of chiral molecules at a wider pH range.