chapter  8
40 Pages

Chapter Chiral Separations by Micellar Electrokinetic Chromatography

Surfactant Mixtures ..........................................................................209 8.6 Cyclodextrin-Modi ed MEKC Separations ................................................. 211 8.7 Enantioseparations Using Polymerized Chiral Surfactants ......................... 214 8.8 MEKC with Mass Spectrometric Detection ................................................. 221 References .............................................................................................................. 222

Micellar electrokinetic chromatography (MEKC) is a powerful method for the separation of ionic as well as nonionic solutes [1,2] by capillary electrophoresis (CE). It was originally developed by Terabe et al. [3] in the early 1980s. In MEKC, solute molecules are partitioned between an ionic pseudostationary phase (PSP) and the electrophoretic run buffer, also called background electrolyte (BGE) and are separated according to their different af nities for the PSP. The separation

principle is very similar to high-performance liquid chromatography (HPLC). However, since uncoated fused silica capillaries are used for separations in MEKC as a rule, the electroosmotic ow (EOF) is superimposed on the separation process. MEKC is found to have several advantages over HPLC, e.g., (1) high ef ciency (large theoretical plate count), (2) short analysis time, (3) small sample size (∼1 nL) and buffer quantities, and (4) ease of changing PSP and running media, which make method development easy. Though MEKC has advantages over HPLC in terms of simplicity, resolution, and cost, it suffers from low concentration sensitivity as a consequence of the limited sample volume and short path length for UV-vis detection. The aforementioned advantages, however, have made MEKC attractive for enantiomeric separations. In order to achieve enantiomeric separations, a chiral PSP or a chiral secondary additive must be employed. The importance of chiral separation led to an enormous number of papers based on chiral separation using electrokinetic chromatography (EKC) and other CE-based techniques in the last two decades. Many authors have reviewed the subject [4-45].