Cyclodextrin-mediated enantioseparation in microemulsion electrokinetic chromatography

New Trends in the Quality Control of Enantiomeric Drugs: Quality by Design-Compliant Development of Chiral Capillary Electrophoresis Methods

Capillary electrophoresis (CE) is a potent method for analyzing chiral substances and is commonly used in the enantioseparation and chiral purity control of pharmaceuticals from different matrices. The adoption of Quality by Design (QbD) concepts in analytical method development, optimization and validation is a widespread trend observed in various analytical approaches including chiral CE. The application of Analytical QbD (AQbD) leads to the development of analytical methods based on sound science combined with risk management, and to a well understood process clarifying the influence of method parameters on the analytical output. The Design of Experiments (DoE) method employing chemometric tools is an essential part of QbD-based method development, allowing for the simultaneous evaluation of experimental parameters as well as their interaction. In 2022 the International Council for Harmonization (ICH) released two draft guidelines (ICH Q14 and ICH Q2(R2)) that are intended to encourage more robust analytical procedures. The ICH Q14 guideline intends to harmonize the scientific approaches for analytical procedures’ development, while the Q2(R2) document covers the validation principles for the use of analytical procedures including the recent applications that require multivariate statistical analyses. The aim of this review is to provide an overview of the new prospects for chiral CE method development applied for the enantiomeric purity control of pharmaceuticals using AQbD principles. The review also provides an overview of recent research (2012–2022) on the applicability of CE methods in chiral drug impurity profiling.

Microemulsion Electrokinetic Chromatography

Microemulsion electrokinetic chromatography (MEEKC) is a special mode of capillary electrophoresis employing a microemulsion as carrier electrolyte. Analytes may partition between the aqueous phase of the microemulsion and its oil droplets which act as a pseudostationary phase. The technique is well suited for the separation of neutral species, in which case charged oil droplets (obtained by addition of an anionic or cationic surfactant) are present. A single set of separation parameters may be sufficient for separation of a wide range of analytes belonging to quite different chemical classes. Fine-tuning of resolution and analysis time may be achieved by addition of organic solvents, by changes in the nature of the surfactants (and cosurfactants) used to stabilize the microemulsion, or by various additives that may undergo some additional interactions with the analytes. Besides the separation of neutral analytes (which may be the most important application area of MEEKC), it can also be employed for cationic and/or anionic species. In this chapter, MEEKC conditions are summarized that have proven their reliability for routine analysis. Furthermore, the mechanisms encountered in MEEKC allow an efficient on-capillary preconcentration of analytes, so that the problem of poor concentration sensitivity of ultraviolet absorbance detection is circumvented.