Chiral capillary electrophoresis‐mass spectrometry: Modes and applications

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Abstract
A review is presented to highlight several approaches for coupling capillary electrophoresis (CE) and electrospray ionization‐mass spectrometry (ESI‐MS) for analysis of chiral compounds. A short discussion of commercially available CE‐MS instruments and interface design is followed by a detail review on various modes of chiral CE‐MS. In general, for each CE‐MS mode, the capabilities, applications and limitations for chiral analysis have been pointed out. The first mode, chiral capillary zone electrophoresis‐mass spectrometry (CZE‐MS) in which neutral derivatized cyclodextrins (CDs) are used is possible using either column coupling with voltage switching or a partial‐filling technique (PFT). However, some applications of direct coupling of CZE‐MS mode are also reported. The second mode is a chiral electrokinetic chromatography‐mass spectrometry (EKC‐MS) in which a charged chiral selector such as a sulfated β‐CD or a vancomycin could be conveniently employed. This is because these chiral selectors have a significantly higher countercurrent electrophoretic mobility which prevents the entrance of these selectors into the mass spectrometer. The combination of counter‐migration and PFT demonstrates that this synergism could be successfully applied to chiral analysis of a broader range of compounds. It is well‐known that the on‐line coupling of micellar electrokinetic chromatography to mass spectrometry (MEKC‐MS) is problematic because the high surface activity and nonvolatile nature of conventional surfactant molecules lower the electrospray ionization efficiency. However, a recent report demonstrates that this hyphenation is now possible with the use of molecular micelles. Various MEKC‐ESI‐MS parameters that can be used to optimize both chiral resolution and ESI response are discussed. Finally, two recent examples that demonstrate the feasibility of using either open‐tubular or packed chiral CEC with MS are reviewed. This survey will attempt to cover the state‐of‐the‐art on various modes of CE‐MS from 1998 up to 2002.