Chiral Separation In Capillary Electrophoresis Research Articles

The separation of the enantiomers of diquats by capillary electrophoresis using randomly sulfated cyclodextrins as chiral selectors.

Diquats, derivatives of the widely used herbicide diquat, represent a new class of functional organic molecules. A combination of their special electrochemical properties and axial chirality could potentially result in their important applications in supramolecular chemistry, chiral catalysis, and chiral analysis. However, prior to their practical applications, the diquats have to be prepared in enantiomerically pure forms and the enantiomeric purity of their P- and M-isomers has to be checked. Hence, a chiral capillary electrophoresis (CE) method has been developed and applied for separation of P- and M-enantiomers of 11 new diquats. Fast and better than baseline CE separations of enantiomers of all 11 diquats within a short time 5-7min were achieved using acidic buffer, 22mM NaOH, 35mM H3 PO4 , pH 2.5, as a background electrolyte, and 6mM randomly sulfated α-, β-, and γ-cyclodextrins as chiral selectors. The most successful selector was sulfated γ-cyclodextrin, which baseline separated the enantiomers of all 11 diquats, followed by sulfated β-cyclodextrin and sulfated α-cyclodextrin, which baseline separated enantiomers of 10 and nine diquats, respectively. Using this method, a high enantiopurity degree of the isolated P- and M-enantiomers of three diquats with a defined absolute configuration was confirmed and their migration order was identified.

Novel approaches to the formation of coatings based on gold nanoparticles and albumin for chiral separation in capillary electrophoresis

Combination of properties of gold nanoparticles and bovine serum albumin is promising for the formation of chiral stationary phases enabling high enantioselectivity due to developed surface of coatings and increased chiral selector concentration on the capillary walls. In this work we proposed and compared two approaches to the formation of physically adsorbed multilayer coatings based on citrate-stabilized gold nanoparticles (cGNP) and bovine serum albumin (BSA) for the chiral separation in capillary electrophoresis. In the first approach pre-synthesized cGNP modified with BSA were immobilized on the capillary coated by poly(diallyldimethylammonium chloride) (PDADMAC). PDADMAC polymer was used as a binding layer promoting sorption of the nanoparticles on the capillary surface. It was shown that cGNP-BSA was poorly adsorbed on the capillary surface due to low zeta potential and could not be used for the formation of dense coatings. The second approach included sequential layer-by-layer deposition of PDAMAC and cGNP, resulting in the formation of a dense layer of nanoparticles. The main stage included in-capillary functionalization of cGNP with BSA. Scanning electron microscopy confirmed that the layer-by-layer deposition of modifiers ensured the formation of dense layer of nanoparticles on the capillary surface. The coating was stable in the entire range of pH studied (2–10). The application of such coating allowed reduction of BSA concentration (to 5 μM) in the background electrolyte required for the tryptophan enantiomers separation. It confirms the prospectiveness of combining nanoparticles and chiral selectors for the increase of specific surface area of the capillary inner walls.

Structural characterization of methyl-β-cyclodextrins by high-performance liquid chromatography and nuclear magnetic resonance spectroscopy and effect of their isomeric composition on the capillary electrophoresis enantioseparation of daclatasvir

The separation of daclatasvir and its R,R,R,R-enantiomer was studied by capillary electrophoresis using various randomly methylated β-CDs and the single isomer heptakis(2,6-di-O-methyl)-β-CD (2,6-DM-β-CD) as chiral selectors in an acidic background electrolyte. Opposite enantiomer migration order was observed for randomly substituted CDs compared to 2,6-DM-β-CD as well as methylated β-CDs with different composition according to the specifications of the manufacturers. HPLC and NMR analyses confirmed that the presence of a high 2,6-DM-β-CD content in the CDs enables to achieve the migration order R,R,R,R-enantiomer > daclatasvir. In contrast, products with low 2,6-DM-β-CD isomer content and/or the presence of a large amount of methylated CD isomers, in which d-glucopyranose moieties are not substituted in either position 2 or 6, displayed the opposite enantiomer migration order daclatasvir > R,R,R,R-enantiomer. The study indicated the importance of the type and composition of derivatized CDs on chiral separations in capillary electrophoresis as well as the importance of proper quality control for cyclodextrin manufacturers. Moreover, the observed migration order could be rationalized based on the composition and substitution pattern of the CDs.

Recent advance of novel chiral separation systems in capillary electrophoresis

Chiral analysis has been an important research field in modern separation science because the enantiomers of a racemic compound often show different or even opposite bioactivities. A variety of analytical techniques have been adopted for chiral analysis over the past few decades. In comparison with conventional chromatographic methods (e. g., high-performance liquid chromatography (HPLC), gas chromatography (GC)), capillary electrophoresis (CE) has multiple advantages such as high separation efficiency, low cost, and diverse separation modes, which have made it one of the most promising analytical techniques for enantioseparation in recent years. The simplest process for CE chiral separation is the addition of a chiral selector (e. g., cyclodextrins and their derivatives, polysaccharides, antibiotics, proteins, crown ethers, chiral exchangers, chiral ionic liquids) in a running buffer to create a chiral separation environment. However, with the ever-increasing number of chiral products in the modern industrial society, satisfactory enantioseparation cannot always be achieved with conventional CE methods. Hence, scientists are endeavoring to improve CE chiral methods. The availability of various fundamental operational modes such as capillary zone electrophoresis (CZE), micellar electrokinetic chromatography (MEKC), ligand-exchange capillary electrophoresis (LECE), non-aqueous capillary electrophoresis (NACE), and capillary electrochromatography (CEC) has enabled researchers to realize flexible design of high-performance CE chiral separation systems by altering the CE operations, especially by the modification of various advanced materials. For example, ionic liquids (ILs) are a group of organic salts whose melting points are below 100℃, or more often, close to room temperature. ILs have been demonstrated to be effective modifiers in chiral CE because of their unique physical and chemical properties such as high conductivity, exceptional chemical and thermal stabilities, as well as excellent solubility in both organic and inorganic solvents. Besides, it is feasible to design and synthesize various task-specific ILs by altering their anion-cation combinations. ILs have been employed for CE enantioseparation through various modes such as achiral IL-modified conventional enantioseparation systems, chiral IL synergistic separation systems, chiral IL LECE systems, and IL-based MEKC, or by the development of novel IL chiral selectors. Nanoparticles are another class of materials that have received considerable interest for use in chiral CE. Nanoparticles have many advantages such as unique size effect, good chemical stability, significant mechanical strength, as well as ease of modification. Several studies have demonstrated that the combination of chiral selectors with nanomaterials such as gold nanoparticles, Fe3O4 magnetic nanoparticles, carbon nanotubes, and mesoporous silica nanomaterials is a promising approach to establish an EKC system or a CEC system. In this review, we summarize the current state-of-the-art of novel CE chiral separation systems, including enantioseparation systems based on achiral or chiral ILs, nanomaterials, metal-organic frameworks (MOFs), and deep eutectic solvents, as well as chiral plug-plug partial filling CE. Another important topic of research in chiral CE is the exploration of enantiorecognition mechanisms. Modern mechanistic studies focus on the applications of advanced analytical techniques such as nuclear magnetic resonance (NMR) or molecular simulations with computer technology, instead of the conventional chromatography- or CE-based thermodynamic methods. For example, nuclear Overhauser effect spectroscopy (NOESY) and rotating-frame Overhauser enhancement spectroscopy (ROESY) have attracted attention because they provide critical information about the spatial proximity of the functional groups of chiral selectors and enantiomers. Molecular simulations have also become popular because of their powerful ability to evaluate the selector-selectand interactions, in addition to enabling visualization of the complex structures. The main objective of this paper is to provide a comprehensive review of state-of-the art of CE techniques in the field of chiral analysis, especially during the period 2015-2019. Existing problems with these techniques and future perspectives are also presented.

Qualitative determination of chiral compounds using capillary electrophoresis

As a well-established analytical separation technique, capillary electrophoresis (CE) is widely used in the separation of chiral substances because of its numerous advantages such as high separation efficiency, short analysis time, small sample dosage, and flexible separation modes. In the previous studies, the CE separation mode, selection of the chiral dispersant and improvement of the separation degree of chiral compounds have been reported in detail. Moreover, it is important to determine the quality of chiral substances and confirm the order of enantiomer peaks after successful separation. This paper summarizes the qualitative detection methods for CE chiral compounds, based on whether the separation analysis of chiral compounds depends on the classification of standard materials. There are two common methods for the qualitative determination of chiral substances in CE. One method compares the difference in the peak migration time, while the other compares the change in peak area before and after the addition of a single enantiomer standard. Both methods are accurate and simple to operate. A diverse range of detectors are used in CE. Based on the type of detector, CE analysis based on standard products is divided into optical, mass spectrometric and electrochemical detection modes. Optical detection involves the use of ultraviolet-visible (UV-vis), laser-induced fluorescence (LIF), chemiluminescence (CL) and other detectors. Among these, the UV detector has the advantages of stable performance, simple structure, and high cost performance and it is most widely used in CE detection as one of the fixed commercial detectors. The LIF detector is a kind of fluorescence detector with a laser as an excitation source. It has the advantages of low background and high signal-to-noise ratio, which make it the most sensitive CE detector. However, this detector is expensive and the sample must be able to provide a fluorescence signal. Otherwise, it is necessary to use a derivatization reagent for sample pretreatment, which renders the analysis complicated. The type of detector leads to a difference in the sample pretreatment, and the resulting spectra and qualitative methods for chiral compounds are also widely different. Therefore, we must choose the most suitable detector to be combined with CE depending on the sample properties and experimental requirements. The above mentioned methods require at least one chiral molecular standard of one configuration. However, for many chiral enantiomers, especially some novel chiral drugs, there is no single commercially available standard enantiomer, and even if there is one, it is very expensive. In this case, the available CE chiral separation methods include enzyme digestion, addition of antibodies, and computational methods. Enzyme digestion entails the addition of refers to adding the corresponding degrading enzyme or oxidase into the tested sample, so that qualitative analysis is possible by observing the change in peak area. In the method based on antibody addition, it is necessary to find antibodies that respond to a single enantiomer. Nevertheless, it is difficult to acquire the corresponding digestion enzymes or specific antibodies for most chiral molecules. Hence, the application scope of these two methods is limited. On the other hand, the computational method is a chiral qualitative method that is rapid, economical, and simple to operate, with a wide range of applications. This technique combines the circular dichroism (CD) spectroscopy with theoretical calculations within the premise of CE separation. The underlying principle of this method covers two aspects. On the one hand, all chiral compounds can give CD signals, and a racemic mixture of isomers gives equal signals but with opposite signs. However, in the case of a non-racemic chiral isomer mixture, only the CD signal of the dominant isomers observed. Using the time-dependent density functional theory (TDDFT), the theoretical CD spectrum of a single isomer can be obtained. By comparing the theoretical and experimental spectra, the configuration of the dominant enantiomer is determined. On the other hand, the peak area in electrophoresis is linearly related to the enantiomeric excess in the CE spectrum. By combining CE with CD, accurate separation and qualitative detection of chiral substances can be easily achieved. The method of calculation, independent of the standard, will greatly promote the development of chiral molecular analysis.

Study on improvement of chiral separation of capillary electrophoresis based on cyclodextrin by deep eutectic solvents

For the first time, the mechanism of deep eutectic solvents (DESs) improving chiral separation by capillary electrophoresis has been studied. The capillary electrophoresis chiral separation has been improved by using DESs as the auxiliary additive. Taking tropicamide, homatropine hydrochloride, ofloxacin, atenolol and propranolol hydrochloride as model chiral separation targets and cyclodextrin (CD) as the chiral selector, and the effects of DESs on the chiral separation resolution were investigated on the basis of optimized conditions. The results of fluorescence spectrophotometry and non-aqueous capillary electrophoresis showed that DESs can improve the resolution of the enantiomers, and the coordination mechanism of DESs was also explored. After DESs were added, the resolution of the above enantiomers increased from 1.26, 1.70, 5.10, 1.90, 2.02 to 3.02, 4.10, 6.86, 2.84 and 5.51 respectively, and the binding constant of CD with propranolol hydrochloride increased from 23 M−1 to 142 M−1. The results showed that DESs is an effective auxiliary additive to improve the separation efficiency of capillary electrophoresis with CD as a basic chiral additive.

Enhanced enantioselectivity of native α‐cyclodextrins by the synergy of chiral ionic liquids in capillary electrophoresis

In the cyclodextrins family, the native α-cyclodextrin has almost been abandoned in capillary electrophoresis chiral separation due to its much weaker enantioselectivity compared with β-cyclodextrin and their derivatives. In this work, several amino acid chiral ionic liquids were selected to establish synergistic enantioseparation systems with native α-cyclodextrin. Enhanced enantioselectivities were observed in the chiral ionic liquids/α-cyclodextrin synergistic systems compared with single α-cyclodextrin system. A series of comparison experiments were performed to demonstrate the superiority of the synergistic systems. Primary parameters affecting the enantioseparation were systematically optimized, including the type and concentration of chiral ionic liquids, α-cyclodextrin concentration, buffer pH, and applied voltage. Best separations of the model enantiomers were obtained in a 20mM Tris/H3 PO4 buffer at pH 2.5 containing 3% (m/v) α-cyclodextrin and 30mM tetramethylammonium-l-arginine. The results show that the α-cyclodextrin is also worth our attention when selecting chiral selectors for capillary electrophoresis enantioseparation of specific racemic compound.

Chiral Measurement of Aspartate and Glutamate in Single Neurons by Large-Volume Sample Stacking Capillary Electrophoresis.

d-Amino acids (d-AAs) are endogenous molecules found throughout the metazoan, the functions of which remain poorly understood. Measurements of low abundance and heterogeneously distributed d-AAs in complex biological samples, such as cells and multicellular structures of the central nervous system (CNS), require the implementation of sensitive and selective analytical approaches. In order to measure the d- and l-forms of aspartate and glutamate, we developed and applied a stacking chiral capillary electrophoresis (CE) with laser-induced fluorescence detection method. The achieved online analyte preconcentration led to a 480-fold enhancement of detection sensitivity relative to capillary zone electrophoresis, without impacting separation resolution or analysis time. Additionally, the effects of inorganic ions on sample preconcentration and CE separation were evaluated. The approach enabled the relative quantification of d-aspartate and d-glutamate in individual neurons mechanically isolated from the CNS of the sea slug Aplysia californica, a well characterized neurobiological model. Levels of these structurally similar d-AAs were significantly different in subpopulations of cells collected from the investigated neuronal clusters.

Enantioseparation of amino acids by micellar capillary electrophoresis using binary chiral selectors and determination of D-glutamic acid and D-aspartic acid in rice wine

ABSTRACTA new chiral capillary electrophoresis (CE) analytical method for the determination of six pairs of amino acid enantiomer-derivatized precapillary with 9-fluorenylmethoxycarbonyl chloride (FMOC) was developed. CE separation parameters such as the pH of background electrolyte, the boric acid concentration, the addition of D-fructose and isopropanol, and the effect of new binary chiral selectors on the electropherograms were investigated. Precapillary and in-capillary derivatization was compared as well. The results showed that enantiomeric separations were obtained with enantio-resolution (Rs) ranged from 2.61 to 9.99 for the FMOC-derivatized amino acid enantiomers except alanine with Rs 1.06. Precapillary derivatization method provides overall better Rs for nearly all the targets except FMOC-aspartate with efficiency up to 1.309 × 106 plates and limit of detection (LOD) down to 2.5 μM. This method was successfully applied to analyze the concentration of the D/L-glutamic acid and D/L-aspartate in seven rice wine samples.

Synthesis of methoxetamine, its metabolites and deuterium labelled analog as analytical standards and their HPLC and chiral capillary electrophoresis separation

Methoxetamine, a designer drug marketed as a replacement for the dissociative anaesthetic ketamine, has been associated with significant numbers of hospital related intoxications and deaths in Europe.

Establishment and Evaluation of the Novel Tetramethylammonium-L-Hydroxyproline Chiral Ionic Liquid Synergistic System Based on Clindamycin Phosphate for Enantioseparation by Capillary Electrophoresis.

Much attention has been paid to chiral ionic liquids (ILs) in analytical chemistry, especially its application in capillary electrophoresis (CE) enantioseparation. However, the investigation of chiral ionic liquids synergistic systems based on antibiotic chiral selectors has been reported in only one article. In this work, a novel chiral ionic liquid, tetramethylammonium-L-hydroxyproline (TMA-L-Hyp), was applied for the first time in CE chiral separation to evaluate its potential synergistic effect with clindamycin phosphate (CP) as the chiral selector. As observed, significantly improved separation was obtained in this TMA-L-Hyp/CP synergistic system compared to TMA-L-Hyp or a CP single system. Several primary factors that might influence the separation were investigated, including CP concentration, TMA-L-Hyp concentration, buffer pH, types and concentrations of organic modifier, applied voltage, and capillary temperature. The best results were obtained with a 40 mM borax buffer (pH 7.6) containing 30 mM TMA-L-Hyp, 80 mM CP, and 20% (v/v) methanol, while the applied voltage and temperature were set at 20 kV and 20°C, respectively.

Application of coating technology in capillary electrophoresis for chiral separation

Chirality is one of the intrinsic attributes of the nature. Chiral separation and analysis are of great importance in many research fields, such as life science, environmental science, biological engineering and pharmaceutical engineering. Currently, chiral capillary electrophoresis technique used for the enantioselective resolution of different kinds of racemates has become one of the most distinctive research and application fields. However, the adsorption of the analytes (or chiral selectors) on the inner wall of the capillary is a common problem in capillary electrophoresis chiral separation. Coating technology, namely modification of the inner wall of the capillary, is the simplest and most effective way to suppress disadvantageous adsorption, and to improve the separation efficiency and analysis repeatability. In this review, the recent applications of different coating procedures in chiral analysis are presented, and the future developments in this field are also prospected.

Highly sensitive trivalent copper chelate–luminol chemiluminescence system for capillary electrophoresis chiral separation and determination of ofloxacin enantiomers in urine samples

A simple, fast and sensitive capillary electrophoresis (CE) strategy combined with chemiluminescence (CL) detection for analysis of ofloxacin (OF) enantiomers was established in the present work. Sulfonated β-cyclodextrin (β-CD) was used as the chiral additive being added into the running buffer of luminol–diperiodatocuprate (III) (K5[Cu(HIO6)2], DPC) chemiluminescence system. Under the optimum conditions, the proposed method was successfully applied to separation and analysis of OF enantiomers with the detection limits (S/N=3) of 8.0nM and 7.0nM for levofloxacin and dextrofloxacin, respectively. The linear ranges were both 0.010–100μM. The method was utilized for analyzing OF in urine; the results obtained were satisfactory and recoveries were 89.5–110.8%, which demonstrated the reliability of this method. This approach can also be further extended to analyze different commercial OF medicines.

Evaluation of vancomycin-based synergistic system with amino acid ester chiral ionic liquids as additives for enantioseparation of non-steroidal anti-inflamatory drugs by capillary electrophoresis

Recently, chiral ionic liquids (ILs) have drawn increasing attention in chiral separation field; however, few papers reported the application of chiral ILs for chiral separation by capillary electrophoresis (CE), and among the papers, chiral ILs were mainly applied as additives to β-cyclodextrin derivatives systems to establish synergistic systems. The synergistic system based on antibiotics with chiral ILs as additives has never been reported before. In this paper, two chiral ionic liquids (ILs) based on amino acid ester, L-alanine and L-valine tert butyl ester bis (trifluoromethane) sulfonamide, were first applied to evaluate the synergistic effect with antibiotic selector for CE chiral separation. The vancomycin-based synergistic system with chiral ILs as additives was successfully established and investigated for the enantioseparation of naproxen, carprofen, ibuprofen, ketoprofen and pranoprofen. Compared to vancomycin-alone cases, significant improvement of separation for all the analytes was observed. Several parameters, such as type and proportion of organic modifier, composition and pH of buffer, concentration of chiral ILs and vancomycin were systematically investigated, and then evaluated by means of Statistical Product and Service Solutions (SPSS) to research the influences on the synergistic effect. Finally, the established method was successfully applied to test the chiral impurity of naproxen sample.

Cationic cyclodextrin as versatile chiral selector for enantiomeric separation in capillary electrophoresis

A novel cationic cyclodextrin, mono-6A-(3-methoxypropan-1-ammonium)-6A-β-cyclodextrin chloride, has been developed and used as chiral selector in capillary electrophoresis (CE). This chiral selector has three recognition sites: β-CD, ammonium cation and methoxy group in the sidearm to contribute three corresponding driving forces including inclusion complexation, electrostatic interaction and hydrogen bonding. This elegantly designed CD exhibits outstanding enantioselectivities in CE for a wide range of acidic and ampholytic racemates due to the extra hydrogen bonding for the chiral recognition. Under optimum pH 6.0, chiral resolutions over 10 can be readily achieved for acidic racemates with CD concentration below 10mM. This cationic CD exhibits great potential for versatile chiral separation in CE. The finding in this study may be applied to construct new host–guest systems for practical applications.

Chiral capillary electrophoresis–mass spectrometry of tetrahydroisoquinoline-derived neurotoxins: Observation of complex stereoisomerism

Previous studies have shown that certain 1,2,3,4-tetrahydroisoquinoline derivatives (TIQs) are neurotoxins inducing Parkinsonism. Further, individual enantiomers of these toxins such as ( R/ S)-N-methylsalsolinol (( R/ S)-NMSal) possess distinct neurotoxicological properties. In this work, a chiral capillary electrophoresis (CE) method with electrospray ionization-tandem mass spectrometric (ESI-MS/MS) detection was developed for the quantification of TIQ enantiomers. Enantioseparation was achieved with sulfated β-cyclodextrin (sulfated β-CD) as chiral selector. To avoid any potential contamination of MS ionization source by the non-volatile chiral selector, partial filling technique was deployed in the CE separation. TIQ derivatives, including ( R/ S)-6,7-dihydroxy-1-methy-TIQ (salsolinol, Sal), ( R/ S)-1-benzyl-TIQ (BTIQ), and ( R/ S)-NMSal, were base-line resolved with resolution values ( R) ranging from 3 (for Sal) to 4.5 (for BTIQ), which were much better than those reported previously by HPLC methods. ESI-MS/MS detection of the resolved TIQ enantiomers was specific and sensitive (LOD = 1.2 μM for Sal enantiomers). The proposed chiral CE–MS/MS method was used to study in vitro formation of ( R/ S)-NMSal. It was found that NMSal was formed from the incubation of epinine (a dopamine metabolite) with acetaldehyde (a metabolite of alcohol). More interestingly, four isomers of NMSal were separated and detected in the incubation solution. They were identified as ( R)-e.e-NMSal, ( R)-e.a-NMSal, ( S)-e.e-NMSal, and ( S)-e.a-NMSal. This was the first lab evidence that this Parkinsonian neurotoxin exists in multiple isomeric forms.

Ultra-high concentration of amylose for chiral separations in capillary electrophoresis

In the present study, a capillary electrophoresis method using high concentration of amylose solutions as separation medium has been developed with the aid of dimethyl sulfoxide (DMSO) as co-solvent. The best buffer conditions for primaquine, trihexyphenidyl (THP), sulconazole and cetirizine enantiomers were optimized as 20mM sodium phosphate buffer with DMSO/water (40/60, v/v) as solvent at a pH of 3.0, containing 10% (w/v) amylose. Partial-filling and semi-permanent coating techniques were used considering the influences of DMSO on UV detection. High chiral resolution for THP enantiomers was obtained showing good chiral separation capacity of this method. The method showed good linearity (R2>0.998) over the concentration range of 0.50 and 2.00mgL−1 for all the enantiomers. The detection limits for the tested enantiomers were in the range from 0.05 to 0.12mgL−1. The linear calibration models were proven to be adequate for the experimental data by lack-of-fit test. The intra-assay precision, inter-day precision and accuracy were all evaluated to be acceptable. Separation and determination of THP enantiomers in rabbit blood were also carried out.

Capillary Electrophoresis Chiral Separation for Enantiomeric Purity Determination of a Basic Drug in Pharmaceutical Formulations

Capillary electrophoresis using a running buffer composed of β-cyclodextrin as the chiral selector and ethanolamine mesylate at pH 9.6 is being used to monitor the stereochemical stability of a hydrophobic drug, containing two chiral centers, in two different formulated self-emulsifying drug delivery system (SEDDS) products. The separation takes place in less than 25 min. Strategies for enhancing the method reproducibility and detection sensitivity in the lower potency formulation are presented. The results demonstrating the specificity, assay precision, recovery, linearity and range achieved during the method validation experiments are presented in this paper.

Chiral separation in capillary electrophoresis using dual neutral cyclodextrins: Theoretical models of electrophoretic mobility difference and separation selectivity

Simple equations and theoretical models, related to enantioselectivity (kappa) and C, have been developed for prediction of electrophoretic mobility difference (Deltamu) and separation selectivity (alpha) for enantiomers in CE using dual CDs, where alpha and kappa are defined as the ratio of mu and the ratio of binding constant (K) for enantiomers to each CD, respectively, C the CD concentration, and the average K for enantiomers and each CD. Experiments were carried out using dual CDs as beta-CD and dimethyl-beta-cyclodextrin (DM-beta-CD) and test analytes as five pairs of amphetamine drug enantiomers. A change in observed Deltamu and alpha of enantiomers in dual CDs was found to be in excellent agreement with the theoretical models. For example, in comparison with single CD1, dual CDs can enhance Deltamu and alpha up to the maximum value when enantiomers migrate with the same order in CD1 and CD2, and have the value of rho > 1.0, where rho is the enantioselectivity ratio for CD2 to CD1, while worse Deltamu and alpha are obtained for enantiomers with rho < 1.0.

Generic capillary electrophoresis conditions for chiral assay in early pharmaceutical development

Generic capillary electrophoresis (CE) conditions have been implemented for chiral separations in early pharmaceutical development. The chiral CE separations of several pharmaceutical samples at different stages of development, i.e., discovery, process chemistry, and investigative new drug application, have been obtained using sulfated beta-cyclodextrin (CD). Several sulfated beta-CDs have been screened to select an appropriate enantioselective agent. The use of a generic CE method allows for a convenient and rapid chiral recognition of different weak bases, with minimal or no method development. CE using sulfated beta-CD for the chiral separation of N-benzoyl methyl piperazine has been validated for linearity, precision, accuracy, limits of detection and quantitation (LOD, LOQ). Although less sensitive than a specific liquid chromatography method using a Chiralpak AD column, the overall performance of the chiral CE method was found comparable. Validation data demonstrate that a LOD of 0.1%, sufficient to fulfill regulatory requirements, is achievable by chiral CE.