Enantioseparation by CE with vancomycin as chiral selector: Improving the separation performance by dynamic coating of the capillary with poly(dimethylacrylamide)

Past, present, and future developments in enantioselective analysis using capillary electromigration techniques

Enantioseparation of chiral products has become increasingly important in a large diversity of academic and industrial applications. The separation of chiral compounds is inherently challenging and thus requires a suitable analytical technique that can achieve high resolution and sensitivity. In this context, CE has shown remarkable results so far. Chiral CE offers an orthogonal enantioselectivity and is typically considered less costly than chromatographic techniques, since only minute amounts of chiral selectors are needed. Several CE approaches have been developed for chiral analysis, including chiral EKC and chiral CEC. Enantioseparations by EKC benefit from the wide variety of possible pseudostationary phases that can be employed. Chiral CEC, on the other hand, combines chromatographic separation principles with the bulk fluid movement of CE, benefitting from reduced band broadening as compared to pressure-driven systems. Although UV detection is conventionally used for these approaches, MS can also be considered. CE-MS represents a promising alternative due to the increased sensitivity and selectivity, enabling the chiral analysis of complex samples. The potential contamination of the MS ion source in EKC-MS can be overcome using partial-filling and counter-migration techniques. However, chiral analysis using monolithic and open-tubular CEC-MS awaits additional method validation and a dedicated commercial interface. Further efforts in chiral CE are expected toward the improvement of existing techniques, the development of novel pseudostationary phases, and establishing the use of chiral ionic liquids, molecular imprinted polymers, and metal-organic frameworks. These developments will certainly foster the adoption of CE(-MS) as a well-established technique in routine chiral analysis.

Bioanalytical Application of Amino Acid Detection by Capillary Electrophoresis

This chapter illustrates the usefulness of capillary electrophoresis (CE) for the analysis of amino acids, and both normal and chiral separations are covered. In order to provide a general description of the main results and challenges in the biomedical field, some relevant applications and reviews on CE of amino acids are tabulated. Furthermore, some detailed experimental procedures are shown, regarding the CE analysis of amino acids in body fluids, in microdialysate, and released upon hydrolysis of proteins. In particular, the protocols will deal with the following compounds: (1) underivatized aminoacids in blood; (2) γ-Aminobutyric acid, glutamate, and L-Aspartate derivatized with Naphthalene-2,3-dicarboxaldehyde; (3) hydrolysate from bovine serum albumine derivatized with phenylisothiocyanate. By examining these applications on real matrices, the capillary electrophoresis efficiency as tool for Amino Acid analysis can be ascertained.

Application of antibiotics as chiral selectors for capillary electrophoretic enantioseparation of pharmaceuticals: a review

Recent years have witnessed several new trends in chiral separation, for example, the enantiorecognition ability of several new antibiotics has been explored using capillary electrophoresis (CE) prior to HPLC; antibiotics have been employed as chiral selectors (CSs) in a nonaqueous CE (NACE) mode; and several new detection techniques (namely, capacitively coupled contactless conductivity detection) have been used in combination with CE for quantification of enantiomers. On account of these emerging trends, this article aims to review the application of various classes of antibiotics for CE enantioseparation of pharmaceuticals. A detailed account of the basic factors affecting enantioseparation, certain limitations of antibiotics as CSs and strategies to mitigate them, and advantages of NACE while using antibiotics as CSs has also been presented.

On-line sample preconcentration by sweeping and poly(ethylene oxide)-mediated stacking for simultaneous analysis of nine pairs of amino acid enantiomers in capillary electrophoresis

This study proposes a sensitive method for the simultaneous separation and concentration of 9 pairs of amino acid enantiomers by combining poly(ethylene oxide) (PEO)-based stacking, β-cyclodextrin (β-CD)-mediated micellar electrokinetic chromatography (MEKC), and 9-fluoroenylmethyl chloroformate (FMOC) derivatization. The 9 pairs of FMOC-derivatized amino acid enantiomers were baseline separated using a discontinuous system, and the buffer vials contained a solution of 150 mM Tris-borate (TB), 12.5% (v/v) isopropanol (IPA), 0.5% (w/v) PEO, 35 mM sodium taurodeoxycholate (STDC), and 35 mM β-CD, and the capillary was filled with a solution of 1.5 M TB, 12.5% (v/v) IPA, 35 mM STDC, and 35 mM β-CD. Based on the difference in viscosity between the sample zone and PEO solution and because of the STDC sweeping, the discontinuous system effectively stacked 670 nL of the 9 pairs of FMOC-derivatized amino acid enantiomers without losing chiral resolution. Consequently, the limits of detection for the 9 pairs of FMOC-derivatized amino acid enantiomers were reduced to 40-60 nM. This method was successfully used to determine d-Tryptophan (Trp), l-Trp, d-Phenylalanine (Phe), l-Phe, d-Glutamic acid (Glu), and l-Glu in various types of beers.

Separation of ketoprofen enantiomers at nanomolar concentration levels by micellar electrokinetic chromatography with on-line electrokinetic preconcentration

Abstract Separation of enantiomers represents an extremely important task in the field of analytical chemistry. This paper contributes to the field of the on-line preconcentration of enantiomers by developing a novel setup based on the electrokinetic accumulation of ketoprofen enantiomers on the pH boundary followed by enantioselective mobilization by a mixture of SDS, sulfated-β-cyclodextrin (S-β-CD), and trimethyl-β-cyclodextrin (TM-β-CD). Under the best conditions, where the injection electrolyte was composed of 50 mmol L−1 borate/NaOH pH 9.5 with 60% (v/v) methanol, the background electrolyte contained 50 mmol L−1 phosphate/NaOH pH 2.5, and the mobilization electrolyte consisted of 50 mmol L−1 phosphate/NaOH pH 2.5 with 4.0% (w/v) S-β-CD, 0.5% (w/v) TM-β-CD, and 20 mmol L−1 SDS, the determination of nanomolar concentration levels of ketoprofen enantiomers was successful by using micellar electrokinetic chromatography with a common UV detection. LODs were 2.5 nmol L−1 and 3.4 nmol L−1, which represent enhancement factors of 9921 and 8529, respectively. The method was also applied to the determination of ketoprofen enantiomers in waste water samples by using simple filtration as a clean-up step. Here, the recovery of ketoprofen enantiomers was 91% at the concentration level of 5×10−9 mol L−1. Graphical abstract

Use of macrocyclic antibiotics as the chiral selectors in capillary electrophoresis

Macrocyclic antibiotics, especially vancomycin, represent a class of versatile chiral selectors for enantioseparations by capillary electrophoresis (CE). In this chapter, we describe the protocol for performing CE enantioseparations with vancomycin as the chiral selector. Dynamic coating of the capillary with polymers including the positively charged polyelectrolyte hexadimethrine bromide or electro-neutral poly(dimethylacrylamide) proved to be very useful in order to reduce the adsorption of vancomycin onto the capillary wall resulting in an improved separation efficiency. The partial filling technique is employed for improvement of the detection sensitivity. Utilization of these techniques makes the CE enantioseparation with vancomycin more practical and robust.

An enzyme immobilized microassay in capillary electrophoresis for characterization and inhibition studies of alkaline phosphatases

A simple and fast dynamically coated capillary electrophoretic method was developed for the characterization and inhibition studies of alkaline phosphatases(EC 3.1.3.1). An inside capillary enzymatic reaction was performed, and hydrolysis of the substrate 4-nitrophenylphosphate to 4-nitrophenol was measured. Fused-silica capillary surface was dynamically modified with polycationic polybrene coating. By reversal of the electroosmotic flow (EOF), analysis time was reduced up to 3 min as the anionic analytes were migrated in the same direction as the EOF. Furthermore, the sensitivity of the method was increased using electroinjection through high-field amplified injection. The baseline separation of 4-nitrophenylphosphate and 4-nitrophenol was achieved by employing 50 mM sodium phosphate as the running buffer (pH 8.5), 0.0025% polybrene, and a constant voltage of -15 kV, and the products were detected at 322 nm. Under the optimized conditions, a good separation with high efficiency was achieved. The new method was applied to study enzyme kinetics and inhibitor screening. K(m) and K(i) values obtained with the new CE method were compared well with the standard spectrophotometric method. Dynamic coating of fused-silica capillary gave fast and reproducible separation of substrate and product. The method can be easily optimized for inhibition studies of other isozymes.

Recent advances of enantioseparations in capillary electrophoresis and capillary electrochromatography

A comprehensive survey of recent developments and applications of capillary electromigration techniques for enantioseparations from January 2006 to June 2010 is presented. The techniques include capillary electrophoresis, chip capillary electrophoresis and capillary electrochromatography. The separation principles and the chiral recognition mechanisms are discussed. Additionally, on-line preconcentrations in chiral capillary electrophoresis are also reviewed.

Enantioseparation of dansyl amino acids by HPLC on a monolithic column dynamically coated with a vancomycin derivative

In this work a chiral stationary phase was prepared by dynamically coating a monolithic reversed-phase HPLC column with a vancomycin-derivative as chiral selector. A hydrophobic alkyl-chain was attached to the vancomycin molecule, providing the immobilization of the chiral selector on the reversed-phase material. Dansyl amino acids were chosen as model analytes for testing the separation power of the dynamically coated phase. All investigated compounds were separated into their enantiomers. Compared with a conventionally packed vancomycin-CSP, a reversal of the enantiomer elution order was obtained.

Chiral analysis of pharmaceuticals by capillary electrophoresis using antibiotics as chiral selectors

The review summarizes the use of the chiral capillary electrophoresis (CE) with different class of antibiotics as chiral selectors in the pharmaceutical field. Basic factors influencing the enantioseparation are shortly discussed. Non-aqueous capillary electrophoresis is also included as well as the coupling of CE to MS. The selection of a chiral selector according the ionic state and structure of the analyte is described. Summary of pharmaceutical applications of chiral CE is given.

Advanced CE for chiral analysis of drugs, metabolites, and biomarkers in biological samples

An analysis of recent trends indicates that CE can show real advantages over chromatographic methods in ultratrace enantioselective determination of biologically active compounds in complex biological matrices. It is due to high separation efficiency and many applicable in-capillary electromigration effects in CE (countercurrent migration, stacking effects) enhancing significantly (enantio)separability and enabling effective sample preparation (preconcentration, purification, analyte derivatization). Other possible on-line combinations of CE, such as column coupled CE-CE techniques and implementation of nonelectrophoretic techniques (extraction, membrane filtration, flow injection) into CE, offer additional approaches for highly effective sample preparation and separation. CE matured to a highly flexible and compatible technique enabling its hyphenation with powerful detection systems allowing extremely sensitive detection (e.g. LIF) and/or structural characterization of analytes (e.g. MS). Within the last decade, more as well as less conventional analytical on-line approaches have been effectively utilized in this field and their practical potentialities are demonstrated on many new application examples in this article. Here, three basic areas of (enantioselective) drug bioanalysis are highlighted and supported by a brief theoretical description of each individual approach in a compact review structure (to create integrated view on the topic), including (i) progressive enantioseparation approaches and new enantioselective agents, (ii) in-capillary sample preparation (preconcentration, purification, derivatization), and (iii) detection possibilities related to enhanced sensitivity and structural characterization.

Enantiorecognition of profens by capillary electrophoresis using a novel chiral selector eremomycin

The evaluation of a macrocyclic glycopeptide antibiotic, eremomycin, as a chiral selector in capillary electrophoresis (CE) has been performed. The stability of eremomycin in solution and capillary electrolyte, as well as its optical and electrophoretic properties have been discussed. The effect of experimental parameters influencing the enantioseparation of several profens has been studied. Excellent enantioseparation of profens has been achieved and migration order has been validated. Comparison of enantioseparations of profens in CE by using eremomycin-mediated electrolytes and in HPLC with eremomycin immobilized on silica has revealed similar trends for both methods.