Strategy for the chiral separation of non-acidic pharmaceuticals using capillary electrochromatography

Enantiomers separation by capillary electrochromatography using polysaccharide-based stationary phases

The separation of chiral compounds is an interesting and important topic of research because these compounds are involved in some biological processes, fundamentally in human health. Among the various application fields where enantiomers are remarkable, drug analysis has to be considered. Most of the drugs contain enantiomers and very often one of the two isomers could be pharmacologically more active or even dangerous. Therefore, the separation of these compounds is very important. Among the different analytical techniques usually employed, capillary electrochromatography has demonstrated great capability in enantiomers resolution. The great potential of this electromigration technique stands mainly in its high efficiency due to the use of an electrosmotic flow (flat flow profile) and on the high selectivity because of the use of a stationary phase. Chiral separation can be obtained utilizing several chiral stationary phases including a polysaccharide derivative. The aim of this review paper is to summarize the main features of capillary electrochromatography and polysaccharide derivatives of chiral stationary phase. It also report examples of practical applications utilizing this approach.

Enantioseparations of pharmaceuticals with capillary electrochromatography: A review

The chiral separation of pharmaceuticals is one of the major research topics in the pharmaceutical industry. Chromatographic techniques are most frequently used in this context. Separations in capillary electrochromatography (CEC) are an alternative and achieved by chromatographic retention and electrophoretic mobility principles. As a result, CEC is characterized by a high selectivity and efficiency. The limited number of stationary phases specifically developed for CEC, the low number of commercially available CEC columns, the frits to maintain the stationary phase, which forms fragile spots in the columns, and the limited column robustness and reproducibility, make CEC not very attractive for industrial application. However, CEC is still applied and studied in the academic field. This review discusses the enantioseparation of drugs in CEC published during the last four years, with a critical view on the reproducibility and the practical utility of these applications.

Experimental design methodologies in the optimization of chiral CE or CEC separations: an overview

In this chapter, an overview of experimental designs to develop chiral capillary electrophoresis (CE) and capillary electrochromatographic (CEC) methods is presented. Method development is generally divided into technique selection, method optimization, and method validation. In the method optimization part, often two phases can be distinguished, i.e., a screening and an optimization phase. In method validation, the method is evaluated on its fit for purpose. A validation item, also applying experimental designs, is robustness testing. In the screening phase and in robustness testing, screening designs are applied. During the optimization phase, response surface designs are used. The different design types and their application steps are discussed in this chapter and illustrated by examples of chiral CE and CEC methods.

Enantioselective capillary electrochromatography: recent developments and new trends

Since its development in the early 1970s, CEC has been studied quite extensively, but unfortunately its use is still mostly located at an academic level. Reasons for this are the limited availability of commercially available stationary phases (SPs) and columns, along with some practical limitations, such as column fragility, lack of column robustness and reproducibility. Nevertheless, CEC maintains a place among the separation techniques, probably because of its unique feature to combine two separation principles. Also in the field of chiral separations, CEC is often used as a separation technique and already showed its potential for this kind of analyses. This overview will focus on the recent applications, i.e. between 2006 and 2010, in enantioselective analysis by means of CEC. For the selected applications, the used SPs (chiral selectors) and their potential for future method development or screening purposes will be evaluated and critically discussed.

Evaluation of carbon nanostructures as chiral selectors for direct enantiomeric separation of ephedrines by EKC

Single-walled nanotubes and multi-walled nanotubes (MWNTs) have been evaluated as chiral selectors for the enantiomeric separation of ephedrines by using EKC with surfactant-coated carbon nanotubes. The analysed compounds were (+/-)-ephedrine, (+/-)-norephedrine and (+/-)-N-methylephedrine. The potential of those carbon nanostructures as chiral selectors has been evaluated by changing different experimental variables such as pH, addition of organic modifiers, potential and injection time. The capability of MWNTs to resolve enantiomeric mixtures was demonstrated by using partial filling of the capillary with concentrated surfactant-coated MWNTs. Differences in the enantioselectivity were discussed.

Enantiomeric impurity determination of levetiracetam using capillary electrochromatography

CEC was used to develop a method for the enantiomeric excess determination of levetiracetam, an antiepileptic drug. Different types of calibration curve were evaluated for use in the range between 0.01 and 1 mg/mL when aniracetam was used as an internal standard. The method gave comparable results when only the areas of the impurity were used in the calibration curve. The predicted detection and quantification limits from the S/N were 1.1 and 3.6 microg/mL, respectively. However, experimental results showed that LOD and LOQ were underestimated. Repeatability of injection was demonstrated by the RSD values obtained for retention time, resolution, ratios of the areas impurity/internal standard, and areas of impurity and internal standard individually, which were below or equal to 9.30%. The between-days variability experiments indicated that it is better to make a calibration curve daily. The finally selected calibration curves were used to test the accuracy of the developed method on bulk samples and Keppra tablets containing 250 mg levetiracetam. Both selected calibration curves performed similarly. The one using the internal standard information gave overall recoveries between 88 and 118%, while the one using areas gave results between 84 and 118%.