Use of β-cyclodextrin polymer as a chiral selector in capillary electrophoresis

Synthesis and applications of sulfopropyl ether γ-cyclodextrin polymer as chiral selector in capillary electrophoresis

A novel sulfopropyl ether γ-cyclodextrin polymer (SPE-γ-CDP) through polycondensating sulfated cyclodextrins (SCDs) was synthesized. This synthesis approach also has the potential of preparing other derived cyclodextrins (CDs) polymers. The polymerized SCDs took on both the properties of SCDs and certain characteristics of polymers, such as chiral selectivity and high viscosity. Synthesis parameters, including reactions sequence, sulfation, and polycondensation conditions were investigated systematically. The product was characterized by elemental analysis, infrared spectroscopy (IR), and indirect UV detections prior to use as background electrolytes additive. The separation conditions, including the concentration of SPE-γ-CDP, the concentration and pH of running buffer, separation voltage, as well as the additional organic solution were optimized during chiral separation of neutral, acidic, and basic enantiomers in capillary electrophoresis (CE). SPE-γ-CDP was proven to be an effective chiral resolving agent in CE with the advantages of simple synthesis process, low cost, similar ratio of charge-to-mass, low current, great reproducibility, and reusability. Graphical Abstract Synthesis and applications of sulfopropyl ether γ-cyclodextrin polymer.

Box-Behnken design for the optimization of an enantioselective method for the simultaneous analysis of propranolol and 4-hydroxypropranolol by CE

An experimental design optimization (Box-Behnken design, BBD) was used to develop a CE method for the simultaneous resolution of propranolol (Prop) and 4-hydroxypropranolol enantiomers and acetaminophen (internal standard). The method was optimized using an uncoated fused silica capillary, carboxymethyl-beta-cyclodextrin (CM-beta-CD) as chiral selector and triethylamine/phosphoric acid buffer in alkaline conditions. A BBD for four factors was selected to observe the effects of buffer electrolyte concentration, pH, CM-beta-CD concentration and voltage on separation responses. Each factor was studied at three levels: high, central and low, and three center points were added. The buffer electrolyte concentration ranged from 25 to 75 mM, the pH ranged from 8 to 9, the CM-beta-CD concentration ranged from 3.5 to 4.5% w/v, and the applied run voltage ranged from 14 to 20 kV. The responses evaluated were resolution and migration time for the last peak. The obtained responses were processed by Minitab to evaluate the significance of the effects and to find the optimum analysis conditions. The best results were obtained using 4% w/v CM-beta-CD in 25 mM triethylamine/H3PO4 buffer at pH 9 as running electrolyte and 17 kV of voltage. Resolution values of 1.98 and 1.95 were obtained for Prop and 4-hydroxypropranolol enantiomers, respectively. The total analysis time was around of 15 min. The BBD showed to be an adequate design for the development of a CE method, resulting in a rapid and efficient optimization of the pH and concentration of the buffer, cyclodextrin concentration and applied voltage.

Characterization of the stereoselective biotransformation of ketamine to norketaminevia determination of their enantiomers in equine plasma by capillary electrophoresis

A robust CE method for the simultaneous determination of the enantiomers of ketamine and norketamine in equine plasma is described. It is based upon liquid-liquid extraction of ketamine and norketamine at alkaline pH from 1 mL plasma followed by analysis of the reconstituted extract by CE in the presence of a pH 2.5 Tris-phosphate buffer containing 10 mg/mL highly sulfated beta-CD as chiral selector. Enantiomer plasma levels between 0.04 and 2.5 microg/mL are shown to provide linear calibration graphs. Intraday and interday precisions evaluated from peak area ratios (n = 5) at the lowest calibrator concentration are < 8 and < 14%, respectively. The LOD for all enantiomers is 0.01 microg/mL. After i.v. bolus administration of 2.2 mg/kg racemic ketamine, the assay is demonstrated to provide reliable data for plasma samples of ponies under isoflurane anesthesia, of ponies premedicated with xylazine, and of one horse that received romifidine, L-methadone, guaifenisine, and isoflurane. In animals not premedicated with xylazine, the ketamine N-demethylation is demonstrated to be enantioselective. The concentrations of the two ketamine enantiomers in plasma are equal whereas S-norketamine is found in a larger amount than R-norketamine. In the group receiving xylazine, data obtained do not reveal this stereoselectivity.

Rapid stereoselective separations of amphetamine derivatives with highly sulfated γ-cyclodextrin

The highly sulfated gamma-CD (HS-gamma-CD) is a chiral selector widely used in CE for the enantioseparation of pharmaceutical compounds. This paper investigated different approaches to reduce the stereoselective analysis time of amphetamine (AT) derivatives according to the chiral selector concentration in the BGE. With high HS-gamma-CD concentration, tested analytes were separated in 3.5 min as anionic complexes with short-end injection technique in reversed polarity mode. However, this procedure presented some limitations in terms of efficiency and resolution, excessive Joule heating and poor compatibility with MS detection. With low HS-gamma-CD concentration, compounds were separated as cations. Conventional approaches to reduce CE analysis time demonstrated critical resolution between some analytes. Therefore, the use of the partial-filling technique compatible with MS detection was carried out. Under optimized conditions, the analysis time for the chiral separation of seven AT like compounds was reduced to 6 min. Moreover, sensitivity of CE-MS was sufficient for the determination of ATs in plasma following a simple liquid-liquid extraction.

Recent developments in chiral capillary electrophoresis and applications of this technique to pharmaceutical and biomedical analysis

This paper provides an overview of the current status of chiral capillary electrophoresis (CE). The emphasis is placed on the application of CE in chiral separation of various racemic compounds. During the last two years about 280 papers, several review articles, and two entire issues, edited by S. Fanali (Electrophoresis 1999, 20, 2577-2798, and H. Nishi and S. Terabe (J. Chromatogr. A 2000, 879, 1-471.) have been devoted to chiral CE. Enantiomeric separations of various compounds, e.g., pharmaceuticals, drug candidates, drugs and related metabolites in biological fluids, amino acids, di- and tri peptides, pesticides and fungicides, have been performed using different chiral selectors. Native and derivatized cyclodextrins continue to be the most widely used chiral selectors. Other chiral selectors such as natural and synthetic chiral micelles, crown ethers, chiral ligands, proteins, oligo- and polysaccharides, and macrocyclic antibiotics have also been applied to chiral CE separations.

Determination of terbutaline enantiomers in human urine by coupled achiral-chiral high-performance liquid chromatography with fluorescence detection

A coupled achiral-chiral high-performance liquid chromatographic system with fluorescence detection at excitation/emission wavelengths of 276/306 nm has been developed for the determination of the enantiomers of terbutaline, (S)-(+)-terbutaline and (R)-(-)-terbutaline in urine. Urine samples were prepared by solid-phase extraction with Sep-pak silica, followed by HPLC. The terbutaline was preseparated from the interfering components in urine on Phenomenex silica column and the terbutaline enantiomers and betaxolol were resolved and determined on a Sumichiral OA-4900 chiral stationary phase. The two columns were connected by a switching valve equipped with silica precolumn. The precolumn was used to concentrate the terbutaline in the eluent from the achiral column before back flushing onto the chiral phase. For each enantiomer the assay was linear between 1 and 250 ng/ml (R2=0.9999) and the detection limit was 0.3 ng/ml. The intra-day variation was between 4.6 and 11.6% in relation to the measured concentration and the inter-day variation was 4.3-11.0%. It has been applied to the determination of (S)-(+)-terbutaline and (R)-(-)-terbutaline in urine from a healthy volunteer dosed with racemic terbutaline sulfate.

Enantioseparations in capillary electromigration techniques: recent developments and future trends

This review summarizes the current status of enantioseparations using capillary electromigration techniques and gives the authors insights on the selected fundamental aspects and future trends in this field. The most recent developments in the field of chiral separations using capillary electrophoresis (CE) and capillary electrochromatography (CEC) are summarized. The status of chiral electromigration techniques is evaluated tacking into account the most recent developments in related techniques such as chiral HPLC, GC and SFC.

Determination of terbutaline enantiomers in human plasma by coupled achiral-chiral high performance liquid chromatography

Achiral-chiral column switching HPLC assay was developed to allow the separation and quantification of the enantiomers of terbutaline in human plasma by means of fluorescence detection. Plasma samples were prepared by solid-phase extraction with sep-pak silica, followed by HPLC assay. The enantiomers of terbutaline and the internal standard were separated from the biological matrix on a silica column, and the two enantiomers were resolved and quantified on a Sumichiral OA-4900 column. The two columns were connected by a switching valve equipped with silica trap column. The trap column was used to concentrate the terbutaline in the eluent from the achiral column before back flushing onto the chiral phase. For each enantiomers, the assay was linear between 2.5-125 ng/ml (r=0.9999) and detection limit was 1.0 ng/ml.

Enantioselective determination by capillary electrophoresis with cyclodextrins as chiral selectors

This review surveys the separation of enantiomers by capillary electrophoresis using cyclodextrins as chiral selector. Cyclodextrins or their derivatives have been widely employed for the direct chiral resolution of a wide number of enantiomers, mainly of pharmaceutical interest, selected examples are reported in the tables. For method optimisation, several parameters influencing the enantioresolution, e.g., cyclodextrin type and concentration, buffer pH and composition, presence of organic solvents or complexing additives in the buffer were considered and discussed. Finally, selected applications to real samples such as pharmaceutical formulations, biological and medical samples are also discussed.

Enantioseparation of atropine by capillary electrophoresis using sulfated beta-cyclodextrin: application to a plant extract

A capillary zone electrophoresis (CZE) method, with sulfated beta-CD as chiral selector, was optimized by means of an experimental design for the enantioseparation of atropine. In this study, a central composite design was used and the following factors were varied simultaneously: buffer concentration, buffer pH and sulfated beta-CD concentration. The resolutions between littorine and its positional isomer ((-)-hyoscyamine) and between atropine enantiomers, as well as the separation time and generated current were established as responses. A model was obtained for each response by linear multiple regression of a second-degree mathematical expression. The most favorable conditions were determined by maximizing the resolution between atropine enantiomers and by setting the other responses at threshold values. Successful results were obtained with a 55 mM phosphate buffer at pH 7 in the presence of 2.9 mM sulfated-beta-CD at 20 degrees C and 20 kV. Under these optimized conditions, a baseline separation of littorine and atropine enantiomers was achieved in less than 5 min. Finally, the method allowed the enantiomeric separation of atropine in a pharmaceutical formulation and was also found to be suitable for the enantiomeric purity evaluation of (-)-hyoscyamine in plant extracts, in relation with the extraction procedure. It was demonstrated that supercritical fluid extraction induced less racemization than classical liquid-solid extraction procedures.

Rapid development of the enantiomeric separation of beta-blockers by capillary electrophoresis using an experimental design approach

A rapid method for determining the separation conditions for chiral resolution of eleven beta-blocking drug substances by capillary electrophoresis is described, using an experimental design approach. An acidic phosphate-triethanolamine buffer and an uncoated fused-silica capillary were used for all experiments. Several modified cyclodextrins were applied as chiral selectors: sulfobutyl ether beta-cyclodextrin (SBE-beta CD), dimethyl beta-cyclodextrin (DM-beta CD), carboxymethyl beta-cyclodextrin (CM-beta CD), and hydroxypropyl beta-cyclodextrin (HP-beta CD). Two different fractional factorial experimental designs were applied: (1) a design examining four factors at three levels (3(4-2)) and (2) one examining three factors at two levels (2(3-1)). The factors studied were: type of cyclodextrin, cyclodextrin concentration, pH of the background electrolyte and percentage of organic modifier. Enough resolution for the separation of the enantiomers and even for their quantification was reached. The same scheme is proposed when a fast chiral separation method needs to be developed for other drug families.

Enantiomeric separations of dansyl amino acids using the macrocyclic antibiotic A35512B as a chiral selector in capillary electrophoresis

The macrocyclic antibiotic A35512B was examined as a chiral selector for capillary electrophoresis (CE) using thirteen racemic dansyl amino acids as test analytes. The chiral selectivity of A35512B was evaluated as a function of the run buffer pH, antibiotic concentration, and organic modifier composition. After optimizing these parameters, the macrocylic antibiotic A35512B provided high resolutions of all the enantiomers for the thirteen dansyl amino acids tested in this study.

Determination of chiral pharmaceutical compounds, terbutaline, ketamine and propranolol, by on-line capillary electrophoresis-electrospray ionization mass spectrometry

On-line capillary electrophoresis-electrospray ionization mass spectrometry (CE-ESI-MS) has been employed for the determination of racemic mixtures of the chiral drugs, terbutaline, ketamine, and propranolol. Separation of the different chiral forms has been achieved by introducing cyclodextrins (CDs), which act as chiral selectors, into the CE operating electrolytes. Cyclodextrins function as chiral selectors in CE because of their ability to form host-guest complexes (inclusion complexes) of varying stability with an array of chiral drugs and other compounds. Derivatized forms of beta-CD (i.e., dimethyl-beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin) were used in this study due to their higher solubilities in the aqueous methanolic operating electrolyte than native beta-CD. Addition of minor quantities of methanol to the aqueous-based CE operating electrolytes improved the stability of electrospray ionization conditions and further enhanced CE resolution of the enantiomeric pairs relative to purely aqueous systems. Introduction of the CDs into the CE operating electrolytes caused suppression of analyte signals in ESI-MS, and the dependence of analyte signal intensities on the solution concentrations of the derivatized beta-CDs was examined. Under optimized conditions, the different enantiomeric forms of the compounds under investigation were successfully separated and detected by CE-ESI-MS.

Enantiomeric separation of propranolol and selected metabolites by using capillary electrophoresis with hydroxypropyl-beta-cyclodextrin as chiral selector

A capillary electrophoresis (CE) investigation of the enantiomeric separation of propranolol and some of its metabolites using CE was undertaken. Resolution of the enantiomers was achieved using hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as the chiral selector. Parameters found to influence separation include cyclodextrin concentration, potential, pH and organic solvent/additive. It was observed that 17 mM HP-beta-CD gave optimum separation over the concentration range used in this study, however different racemates appear to have best resolution at different CD concentration. The potential does not have a great effect on enantiomer resolution, but appears to cause relative metabolite migration times to alter such that separation is affected. Carrier pH affects both migration time, and enantiomer resolution and metabolite separation. Above pH 5 inferior results are obtained. This is the first report of enantiomeric resolution of propranolol metabolites using CE.

Enantioselectivity in chiral capillary electrophoresis with polysaccharides

This review surveys enantiomer separation by capillary electrophoresis (CE) using polysaccharides as chiral selectors. Many ionic or electrically neutral polysaccharides, such as heparin, chondroitin sulfate, dextrin, etc., have been employed successfully for the CE separation of enantiomers. The operational conditions that affect the enantioselectivity of the chiral separation system will be described. The mechanism of enantioseparation will also be discussed briefly.

Controlling enantioselectivity in chiral capillary electrophoresis with inclusion-complexation

The separation of chiral compounds is of key importance in different fields of application, e.g., pharmaceutical, industrial, forensic, biological, clinical etc. Capillary electrophoresis (CE) is a powerful analytical method applied in chiral analysis and inclusion-complexation is one of the most frequently used mechanism to improve the selectivity of the enantiomeric separation. Cyclodextrins and their derivatives or modified crown-ethers have been successfully applied in CE for the enantiomeric separation of a wide number of analytes. This review surveys the separation of enantiomers by CE when chiral selectors, forming inclusion-complexation, are used. The control of enantioselectivity can be done carefully by considering several experimental parameters such as chiral selector type and concentration, pH, ionic strength and concentration of the background electrolyte, electroosmotic flow, organic modifier etc. The review presents a list of the latest separation of enantiomers by CE where inclusion-complexation plays a key role in the stereoselective separation mechanism.

Enantioseparation of local anaesthetic drugs by capillary zone electrophoresis with cyclodextrins as chiral selectors using a partial filling technique

The enantiomers of prilocaine were successfully resolved with alpha-cyclodextrin, and those of mepivacaine and bupivacaine, with methyl-beta-cyclodextrin as chiral selectors, by means of capillary zone electrophoresis (CZE) employing a partial filling technique. By this separation mode, a discontinous separation zone is formed in the capillary. Prior to application of the actual drug substance, the capillary is partially filled with the separation solution. During the enantioseparation both ends of the capillary are dipped into the running buffer solution, i.e., without chiral selector. The consumption of chiral selector is thus very low, less than a microliter per run. The repeatibility of the electrophoretic mobility of the enantiomers was better than 1.2% relative standard deviation (RSD). The effect of the length of the separation zone on the resolution of the enantiomers was studied. The application time of the chiral selector, instead of the selector concentration, was varied in order to improve and regulate the enantioresolution and reduce consumption of the chiral selector as much as possible. It was found that the enantioseparations were directly affected by the length of the separation zone, and there was a minimal plug length where complete enantioresolution was achieved.

Identification of chiral drug isomers by capillary electrophoresis

Separation of optical isomers of compounds of pharmaceutical interest by capillary electrophoretic techniques is reviewed. The direct and indirect separation method, as well as the main resolution mechanisms and the parameters influencing the stereoselectivity are discussed considering capillary zone electrophoresis, micellar electrokinetic chromatography, isotachophoresis and electrochromatography. Several chiral selectors have been successfully used in CE for chiral separation, including cyclodextrins and their derivatives, modified crown-ethers, proteins, antibiotics, linear saccharides and chiral surfactants. Only applications in the pharmaceutical field with the most important experimental conditions are summarised in the Tables reported in this paper. The chiral analyses of drugs in real samples like biological fluids or pharmaceutical formulations are also reported.

Capillary electrophoresis of cardiovascular drugs

This review surveys the use of capillary electrophoresis for the analysis of cardiovascular drugs. Each section presents examples of separations according to the class of the cardiovascular agent. The classes presented are beta-adrenergic antagonists (beta-blockers), acetylcholinesterase inhibitors, angiotensin-converting enzyme inhibitors, dieuretics, alpha-adrenergic antagonists, calcium channel blockers, cardiac glycosides, hypolipidemics (HmG-CoA reductase inhibitors and fibric acid), vasodilators and sodium channel blockers. Examples of the separation modes discussed include capillary electrophoresis, micellar electrokinetic chromatography using many additives (e.g. sodium dodecyl sulfate, cyclodextrins, bile salts, proteins, oligosaccharides) and isotachophoresis.

Effect of the degree of substitution of cyclodextrin derivatives on chiral separations by high-performance liquid chromatography and capillary electrophoresis

Optical isomers of some basic racemic drugs (oxprenolol, AMEBD, ephedrine) were separated by high-performance liquid chromatography (HPLC) and/or capillary electrophoresis (CE) using carboxymethyl-beta-cyclodextrin (CMBCD) with various degree of substitution (DS). The effects of the separation conditions (pH, concentration and DS of CMBCD) were studied and compared using CE and HPLC. The degree of substitution had a significant effect on the resolution of the optical isomers and the ionic strength of the separation media, hence the use of well characterized CD derivatives is crucial. Different optimum DS values for the same test samples were obtained when HPLC or CE was used.

Further study on the use of uncharged beta-cyclodextrin polymer in capillary electrophoresis: enantiomeric separation of some alpha-hydroxy acids

Uncharged beta-cyclodextrin polymer was used as chiral selector for the enantiomeric separation of some alpha-hydroxy acids by capillary electrophoresis. Complexation and enantiomeric resolution of mandelic acid, m-hydroxy and p-hydroxymandelic acid, 3,4-dihydroxymandelic acid, as well as 2- and 3-phenyllactic acid were studied, changing the concentration of the beta-cyclodextrin polymer added to the background electrolyte at different pH in the range of 4.5-7. Furthermore, the effects of the concentration of the background electrolyte, column temperature, and applied voltage on chiral resolution were also examined. The best enantiomeric separations were obtained using a background electrolyte at pH 6 containing 100 mg/mL of beta-cyclodextrin polymer.