Dispersive micro-solid-phase extraction combined with online preconcentration by capillary electrophoresis for the determination of glycopyrrolate stereoisomers in rat plasma

A simple and sensitive analytical method for four isomers of glycopyrrolate in rat plasma was developed using cation-selective exhaustive injection-sweeping cyclodextrin-modified electrokinetic chromatography (CSEI-Sweeping-CDEKC) for online enrichment combined with dispersive micro-solid-phase extraction pretreatment. The CSEI-Sweeping-CDEKC was conducted on an uncoated fused silica capillary (40.2 cm × 75 μm) with an applied voltage of -20 kV. The electrophoretic analysis was carried out in 30 mM phosphate solution at pH 2.0 containing 20 mg/mL sulfated-β-cyclodextrin and 5% acetonitrile. Under these optimized conditions, the detection limit for racemic glycopyrrolate was found to be 2.0 ng/mL and this method could increase 495-fold detection sensitivity compared with the traditional injection method. Additionally, the parameters that affected the extraction efficiency of dispersive micro-solid-phase extraction were also examined systematically. The glycopyrrolate isomers in rat plasma samples as low as 0.0625 μg/mL were able to be separated and detected by capillary electrophoresis with the aid of CSEI-sweeping. The findings of this study show that the dispersive micro-solid-phase extraction pretreatment coupled with CSEI-Sweeping-CDEKC is a rapid and convenient method for analyzing glycopyrrolate isomers in rat plasma.

Improving the sensitivity in chiral capillary electrophoresis

CE is known for being one of the most powerful analytical techniques when performing enantioseparations due to its numerous advantages such as excellent separation efficiency and extremely low solvents and reagents consumption, all of them derived from the capillary small dimensions. Moreover, it is worth highlighting that unlike in chromatographic techniques, in CE the chiral selector is generally within the separation medium instead of being attached to the separation column which makes the method optimization a more versatile task. Despite its numerous advantages, when using UV-Vis detection, CE lacks of sensitivity detection due to its short optical path length derived from the narrow separation capillary. This issue can be overcome by means of different approaches, either by sample treatment procedures or by in-capillary preconcentration techniques or even by employing detection systems more sensitive than UV-Vis, such as LIF or MS. The present review assembles the latest contributions regarding improvements of sensitivity in chiral CE published from June 2013 until May 2015, which follows the works included in a previous review reported by Sánchez-Hernández et al. [Electrophoresis 2014, 35, 12-27].

The application of capillary electrophoresis techniques in toxicological analysis

Capillary electrophoresis (CE) comprises a group of techniques used to separate chemical mixtures. Analytical separation is based on different electrophoretic mobilities, thereby allowing qualitative and quantitative evaluations to be made. The application of CE in medical science, especially in toxicological studies, is developing rapidly because of the short time required for analysis and its high sensitivity, selectivity and ability to determine substances of an acidic, alkaline and neutral character. This review focuses on the possibility of applying CE in toxicological analysis. Advances in different CE analyses and detection techniques connected with this method are described.

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.

Chiral derivatizations applied for the separation of unusual amino acid enantiomers by liquid chromatography and related techniques

Amino acids are essential for life, and have many functions in metabolism. One particularly important function is to serve as the building blocks of peptides and proteins, giving rise complex three dimensional structures through disulfide bonds or crosslinked amino acids. Peptides are frequently cyclic and contain proteinogenic as well as nonproteinogenic amino acids in many instances. Since most of the proteinogenic α-amino acids contain at least one stereogenic center (with the exception of glycine), the stereoisomers of all these amino acids and the peptides in which they are to be found may possess differences in biological activity in living systems. The impetus for advances in chiral separation has been highest in the past 25 years and this still continues to be an area of high focus. The important analytical task of the separation of isomers is achieved mainly by chromatographic and electrophoretic methods. This paper reviews indirect separation approaches, i.e. derivatization reactions aimed at creating the basis for the chromatographic resolution of biologically and pharmaceutically important enantiomers of unusual amino acids and related compounds, with emphasis on the literature published from 1980s. The main aspects of the chiral derivatization of amino acids are discussed, i.e. derivatization on the amino group, transforming the molecules into covalently bonded diastereomeric derivatives through the use of homochiral derivatizing agents. The diastereomers formed (amides, urethanes, urea and thiourea derivatives, etc.) can be separated on achiral stationary phases. The applications are considered, and in some cases different derivatizing agents for the resolution of complex mixtures of proteinogenic d,l-amino acids, non-proteinogenic amino acids and peptides/amino acids from peptide syntheses or microorganisms are compared.

New advances in amino acid profiling by capillary electrophoresis-electrospray ionization-mass spectrometry

Capillary electrophoresis-electrospray ionization-mass spectrometry (CE-ESI-MS) offers a selective, sensitive yet robust approach for amino acid profiling in complex biological samples with minimal sample pretreatment. Direct analysis of amino acids and their analogs is routinely performed using strongly acidic buffer conditions under positive-ion mode ESI-MS with a coaxial sheath liquid interface. New advances in online sample preconcentration, chemical derivatization, and/or ESI interface designs can further improve assay performance allowing for resolution of amino acid stereoisomers and labile aminothiols with low nanomolar detection limits. Accurate prediction of the electromigration behavior of amino acids offers a convenient approach for their qualitative identification complementary to ESI-MS. Simultaneous analysis of amino acids together with other classes of cationic metabolites can be realized by CE-ESI-MS for comprehensive metabolite profiling applications relevant to disease prognosis, drug efficacy, and food safety/quality control.

Recent approaches in sensitive enantioseparations by CE

The latest strategies and instrumental improvements for enhancing the detection sensitivity in chiral analysis by CE are reviewed in this work. Following the previous reviews by García-Ruiz et al. (Electrophoresis 2006, 27, 195-212) and Sánchez-Hernández et al. (Electrophoresis 2008, 29, 237-251; Electrophoresis 2010, 31, 28-43), this review includes those papers that were published during the period from June 2009 to May 2011. These works describe the use of offline and online sample treatment techniques, online sample preconcentration techniques based on electrophoretic principles, and alternative detection systems to UV-Vis to increase the detection sensitivity. The application of the above-mentioned strategies, either alone or combined, to improve the sensitivity in the enantiomeric analysis of a broad range of samples, such as pharmaceutical, biological, food and environmental samples, enables to decrease the limits of detection up to 10⁻¹² M. The use of microchips to achieve sensitive chiral separations is also discussed.

Advances in the enantioseparation of β-blocker drugs by capillary electromigration techniques

β-Blocker drugs or β-adrenergic blocking agents are an important class of drugs, prescribed with great frequency. They are used for various diseases, particularly for the treatment of cardiac arrhythmias, cardioprotection after myocardial infarction (heart attack), and hypertension. Almost all β-blocker drugs possess one or more stereogenic centers; however; only some of them are administered as single enantiomers. Since both enantiomers can differ in their pharmacological and toxicological properties, enantioselective analytical methods are required not only for pharmacodynamic and pharmacokinetic studies but also for quality control of pharmaceutical preparations with the determination of enantiomeric purity. In addition to the chromatographic tools, in recent years, capillary electromigration techniques (CE, CEC, and MEKC) have been widely used for enantioselective purposes employing a variety of chiral selectors, e.g. CDs, polysaccharides, macrocyclic antibiotics, proteins, chiral ion-paring agents, etc. The high separation efficiency, rapid analysi,s and low consumption of reagents of electromigration methods make them a very attractive alternative to the conventional chromatographic methods. In this review, the development and applications of electrodriven methods for the enantioseparation of β-blocker drugs are reported. The papers concerning this topic, published from January 2000 until December 2010, are summarised here. Particular attention is given to the coupling of chiral CE and CEC methods to MS, as this detector provides high sensitivity and selectivity.

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.

Separation of Tic-hydantoin enantiomers, potent sigma-1 agonists, by high performance liquid chromatography and capillary electrophoresis

Stereospecific separations of seven Tic-hydantoin sigma-1 agonists were performed by both HPLC method using derivatized cellulose and amylose chiral stationary phases and capillary electrophoresis (CE) method using neutral and anionic cyclodextrins added in the background electrolyte (BGE). An optimal baseline separation (R(s)>3.3 with analysis times<25min) was readily obtained with all silica-based celluloses and amyloses using a normal-phase methodology. CE was used as an alternative technique to HPLC for the Tic-hydantoin derivatives separation. The enantiomers were fully resolved with highly sulfated beta-cyclodextrins at pH 2.5 (R(s)>1.5 with analysis times <11min). Both methods were validated in terms of linearity, detection and quantification limits. They were used to check the enantiomeric purity of the enantiomers.

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.

Direct chiral analysis of primary amine drugs in human urine by single drop microextraction in-line coupled to CE

Three-phase single drop microextraction (SDME) was in-line coupled to chiral CE of weakly basic amine compounds including amphetamine. SDME was used for the matrix isolation and sample preconcentration in order to directly analyze urine samples with the minimal pretreatment of adding NaOH. A small drop of an acidic aqueous acceptor phase covered with a thin layer of octanol was formed at the tip of a capillary by simple manipulation of the liquid handling functions of a commercial CE instrument. While the saline matrix of the urine sample was blocked by the octanol layer, the basic analytes in a basic aqueous donor phase were concentrated into the acidic acceptor drop through the octanol layer by the driving force of the pH difference between the two aqueous phases. The enantiomers of the enriched amines were resolved by using (+)-(18-crown-6)-tetracarboxylic acid as a chiral selector for the subsequent CE separation. From 10 min SDME with the agitation of the donor phase by a small stirrer retrofit to the CE instrument, enrichment factors were about a 1000-fold, yielding the LOD of 0.5 ng/mL for amphetamine. This low LOD value as well as the convenience of in-line coupled SDME make the proposed scheme well suited for the demanding chiral analysis of amphetamine-type stimulants.

Contemporary sample stacking in CE

Sample stacking techniques remain an important tool for enhancement of the selectivity and sensitivity of analyses in contemporary CZE. This contribution reviews new knowledge on this topic published since 2006. It is organized according to the operational principles used, which include concentration adjustment, application of a pH step, MEKC and sweeping, and transient ITP. Techniques combining several of these principles and comparative studies are also included.

Simultaneous coaxial thermal lens spectroscopy and retro-reflected beam interference detection for capillary electrophoresis

A novel optical scheme, which accomplished simultaneous coaxial thermal lens spectroscopy and retro-reflected beam interference detection for capillary electrophoresis, has been described. By a special design, an adjustable pump laser waist relative to the probe laser waist was implemented, while some key elements for both detection modes were optimized. In either detection modes, certain preponderance compared with former reports was indicated. With both coaxial thermal lens spectroscopy and retro-reflected beam interference detection, the reported detection scheme combined high sensitivity and universal property for capillary electrophoresis detection.

Cyclodextrins in capillary electrophoresis enantioseparations--recent developments and applications

Capillary EKC has been established as a versatile and robust CE method for the separation of enantiomers. Within the chiral selectors added to the BGE CDs continue as the most widely used selectors due to their structural variety and commercial availability. This is reflected in the large number of practical applications of CDs to analytical enantioseparations that have been reported between January 2006 and January 2008, the period of time covered by this review. Most of these applications cover aspects of life sciences such as drug analysis, bioanalysis, environmental analysis, or food analysis. Moreover, new CD derivatives have been developed in an attempt to achieve altered enantioselectivities and to further broaden the application range. Finally, efforts will be summarized that aim at an understanding of the molecular level of the chiral recognition between CDs and the analytes.