An extended description of the effect of detergent monomers on migration in micellar electrokinetic chromatography

Strategies for capillary electrophoresis: Method development and validation for pharmaceutical and biological applications-Updated and completely revised edition

This review is in support of the development of selective, precise, fast, and validated capillary electrophoresis (CE) methods. It follows up a similar article from 1998, Wätzig H, Degenhardt M, Kunkel A. "Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications," pointing out which fundamentals are still valid and at the same time showing the enormous achievements in the last 25 years. The structures of both reviews are widely similar, in order to facilitate their simultaneous use. Focusing on pharmaceutical and biological applications, the successful use of CE is now demonstrated by more than 600 carefully selected references. Many of those are recent reviews; therefore, a significant overview about the field is provided. There are extra sections about sample pretreatment related to CE and microchip CE, and a completely revised section about method development for protein analytes and biomolecules in general. The general strategies for method development are summed up with regard to selectivity, efficiency, precision, analysis time, limit of detection, sample pretreatment requirements, and validation.

Formamide as an organic modifier in MEKC with SDS

The effect of formamide (FA) as a modifier on the retention in MEKC with SDS as the detergent was investigated. The mobility of a series of alkylphenones and of a zwitterionic fluorescent compound as a function of the FA and the SDS concentration was determined for this purpose. Buffering electrolyte was borate, pH 9.23, with total ionic strength of 50 mM. The dependence of the mobility on the FA content - up to 63% w/w - of the BGE (at 10 mM SDS) allows the conclusion that the micelles are destabilized, and the CMC is shifted to higher values. In the system containing 33% FA or more no micelles are present anymore, and the retention factors of all compounds tend to zero. In an MEKC system with 27% v/v FA the CMC of SDS is increased from 2.4 mM in the aqueous BGE with the same buffer composition to 9.7 mM, a behavior that is in contrast to electrolyte-free FA-water systems. The partition constants of free analytes and the formation constants of the adduct between analyte and detergent monomer (assuming 1:1 stoichiometry) were derived from the dependence of the mobility on the SDS concentration. In addition, the involved equilibria were extended by that from the distribution of the analyte-monomer adduct between aqueous and micellar phase, and the according partition constants were derived as well. A selective change in the extent of partitioning was observed for the zwitterionic compound. In general, all binding constants were decreased upon addition of FA, though to a different extent. Although the binding constants of the analyte-monomer associate were only slightly influenced, the most pronounced decrease is found for their partitioning into the micelles.