Combined use of l‐alanine tert butyl ester lactate and trimethyl‐β‐cyclodextrin for the enantiomeric separations of 2‐arylpropionic acids nonsteroidal anti‐inflammatory drugs

In this study, a new CE method, employing a binary system of trimethyl‐β‐CD (TM‐β‐CD) and a chiral amino acid ester‐based ionic liquid (AAIL), was developed for the chiral separation of seven 2‐arylpropionic acid nonsteroidal anti‐inflammatory drugs (NSAIDs). In particular, the enantioseparation of ibuprofen, ketoprofen, carprofen, indoprofen, flurbiprofen, naproxen, and fenoprofen was improved significantly by supporting the BGE with the chiral AAIL l ‐alanine tert butyl ester lactate (l ‐AlaC₄Lac). Parameters, such as concentrations of TM‐β‐CD and l ‐AlaC₄Lac, and buffer pH, were systematically examined in order to optimize the chiral separation of each NSAID. It was observed that the addition of the AAIL into the BGE improved both resolution and efficiency significantly. After optimization of separation conditions, baseline separation (R_s>1.5) of five of the analytes was achieved in less than 11 min, while the resolution of ibuprofen and flurbiprofen was approximately 1.2. The optimized enantioseparation conditions for all analytes involve a BGE of 5 mM sodium acetate/acetic acid (pH 5.0), an applied voltage of 30 kV, and a temperature of 20°C. In addition, the results obtained by computing the %‐RSD values of the EOF and the two enantiomer peaks, demonstrated excellent run‐to‐run, batch‐to‐batch, and day‐to‐day reproducibilities.     

Stereoisomer separation of flavanones and flavanone‐7‐O‐glycosides by means of nanoliquid chromatography employing derivatized β‐cyclodextrins as mobile‐phase additive

A nanoliquid chromatographic method for the stereoisomer separation of some flavanone aglycones and 7‐O‐glycosides has been proposed employing a C18 capillary column and a chiral mobile‐phase additive such as cyclodextrin. The chiral separation of eriodictyol, naringenin, and hesperitin was obtained by addition of carboxymethyl‐β‐cyclodextrin to the mobile phase, whereas eriocitrin, naringin, narirutin, and hesperidin diastereoisomers were resolved by using sulfobutyl ether‐β‐cyclodextrin. The influence of the composition of the mobile phase, the length of the capillary column, and the flow rate on the chiral recognition were investigated. At optimum conditions, baseline separation for the selected aglycones and glycosylated forms were achieved with a mobile phase consisting of 50 mM sodium acetate buffer pH 3 and 30% methanol containing 20 mM of carboxymethyl‐β‐cyclodextrin and 10 mM of sulfobutyl ether‐β‐cyclodextrin, respectively. Precision, linearity, and sensitivity of the method were tested. Limits of detection and quantification for the studied flavanone glycosides were in the range 1.3‐2.5 and 7.5‐12.5 µg/mL, respectively. The method was used for the determination of the diastereomeric composition of the flavanone‐7‐O‐glycosides in Citrus juices after solid‐phase extraction procedure.     

Separation and determination of corynoxine and corynoxine B using chiral ionic liquid and hydroxypropyl‐β‐cyclodextrin as additives by field‐amplified sample stacking in capillary electrophoresis

A sensitive, fast, and effective method, field‐amplified sample stacking (FASS) in capillary electrophoresis, has been established for the separation and determination of corynoxine and corynoxine B. Hydroxypropyl‐β‐CD (HP‐β‐CD) and tetrabutylammonium‐L‐glutamic acid (TBA‐L‐Glu) were used as additives in the separation system. Electrokinetic injection was chosen to introduce sample from inlet at 10 kV for 50 s after a water plug (0.5 psi, 4 s) was injected to permit FASS. The running buffer (pH 6.1) was composed of 40 mM sodium dihydrogen phosphate solution, 130 mM HP‐β‐CD, and 10 mM TBA‐L‐Glu and the separation voltage was 20 kV. Under the optimum conditions, corynoxine and corynoxine B were successfully enriched and separated within 12 min and the sensitivity was improved approximately by 700–900 folds. Calibration curves were in a good linear relationship within the range of 62.5–5.00 × 10³ ng/mL for both corynoxine and corynoxine B. The limits of detection (S/N = 3) and quantitation (S/N = 10) were 14.9, 45.2 ng/mL for corynoxine and 11.2, 34.5 ng/mL for corynoxine B, respectively. Finally, this method was successfully applied for the determination of corynoxine and corynoxine B in the stems with hooks of Uncaria rhynchophylla and its formulations.     

Chiral separation of 12 pairs of enantiomers by capillary electrophoresis using heptakis‐(2,3‐diacetyl‐6‐sulfato)‐β‐cyclodextrin as the chiral selector and the elucidation of the chiral recognition mechanism by computational methods

Chiral separation of 12 pairs of basic analyte enantiomers including oxybutynin, bambuterol, tradinterol, clenbuterol, clorprenaline, terbutaline, tulobuterol, citalopram, phencynonate, fexofenadine, salbutamol, and penehyclidine was conducted by capillary electrophoresis using a single‐isomer anionic β‐cyclodextrin derivative, heptakis‐(2,3‐diacetyl‐6‐sulfato)‐β‐cyclodextrin as the chiral selector. Parameters influencing separation were studied, including background electrolyte pH, heptakis‐(2,3‐diacetyl‐6‐sulfato)‐β‐cyclodextrin concentration, buffer concentration, and separation voltage. A background electrolyte consisting of 50 mM Tris‐H₃PO₄ and 6 mM heptakis‐(2,3‐diacetyl‐6‐sulfato)‐β‐cyclodextrin at pH 2.5 was found to be highly efficient for the separation of most enantiomers, with other conditions of normal polarity mode at 10 kV, detection wavelength of 210 nm using hydrodynamic injection for 3 s. Under the optimal conditions, baseline resolution (>1.50) for 11 pairs of enantiomers and somewhat lower resolution for penehyclidine enantiomers (1.17) were generated. Moreover, the possible mechanism of separation of clenbuterol, oxybutynin, salbutamol, and penehyclidine was investigated using a computational modeling method.     

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.     

Enantioselective separation of chiral vicinal diols in capillary electrophoresis using a mono‐6A‐aminoethylamino‐β‐cyclodextrin as a chiral selector

This paper describes an improved access to mono‐6^A‐aminoethylamino‐β‐CD (β‐CDen), a very efficient cationic chiral selector for CZE in the separation of eight chiral aromatic vicinal diols. The β‐CDen concentration has a strong influence on the efficiency of enantioseparation. The effects of the pH and concentration of the BGE, the capillary temperature, and the applied voltage on the resolution and separation selectivity have been studied. Excellent chiral resolution was achieved under the optimal conditions of β‐CDen 10 mM, pH 10, 200 mM borate buffer at 15 kV and 20°C within 20 min. Moreover, the developed method was successfully applied to the determination of the enantiomeric purity of the catalytic asymmetric dihydroxylation (AD) reaction products.     

Chiral separation of phenylalanine and tryptophan by capillary electrophoresis using a mixture of β‐CD and chiral ionic liquid ([TBA] [l‐ASP]) as selectors

In this paper, a simple, effective and green capillary electrophoresis separation and detection method was developed for the quantification of underivatized amino acids (dl ‐phenylalanine; dl ‐tryptophan) using β‐Cyclodextrin and chiral ionic liquid ([TBA] [l ‐ASP]) as selectors. Separation parameters such as buffer concentrations, pH, β‐CD and chiral ionic liquid concentrations and separation voltage were investigated for the enantioseparation in order to achieve the maximum possible resolution. A good separation was achieved in a background electrolyte composed of 15 mm sodium tetraborate, 5 mm β‐CD and 4 mm chiral ionic liquid at pH 9.5, and an applied voltage of 10 kV. Under optimum conditions, linearity was achieved within concentration ranges from 0.08 to 10 µg/mL for the analytes with correlation coefficients from 0.9956 to 0.9998, and the analytes were separated in less than 6 min with efficiencies up to 970,000 plates/m. The proposed method was successfully applied to the determination of amino acid enantiomers in compound amino acids injections, such as 18AA‐I, 18AA‐II and 3AA. Copyright © 2013 John Wiley & Sons, Ltd.     

Enantioseparation of chiral aromatic acids by multiple dual mode counter‐current chromatography using hydroxypropyl‐β‐cyclodextrin as chiral selector

This work concentrates on extending the utilization of multiple dual mode (MDM) counter‐current chromatography in chiral separations. Two aromatic acids, 2‐(6‐methoxy‐2‐naphthyl)propionic acid (NAP) and 2‐phenylpropionic acid (2‐PPA), were enantioseparated by MDM counter‐current chromatography using hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as chiral selector. The two‐phase solvent systems consisting of n‐hexane/ethyl acetate 0.1 mol/L phosphate buffer pH 2.67 containing 0.1 mol/L HP‐β‐CD (7.5:2.5:10 for NAP and 7:3:10 for 2‐PPA, v/v/v) were used. Conventional MDM and modified MDM were compared according to peak resolution under current separation mechanism. The influence of elution time after the first‐phase inversion and number of cycles for MDM were investigated. Peak resolution of NAP and 2‐PPA increased from 0.62 to 1.05 and 0.72 to 0.84, respectively, using optimized MDM conditions. Being an alternative elution method for counter‐current chromatography, MDM elution greatly improved peak resolution in chiral separations.     

Chiral separation of lansoprazole and rabeprazole by capillary electrophoresis using dual cyclodextrin systems

Novel capillary electrophoresis methods using CDs as chiral selectors were developed and validated for the chiral separation of lansoprazole and rabeprazole, two proton pump inhibitors. Fourteen different neutral and anionic CDs were screened at pH 4 and 7 in the preliminary analysis. Sulfobutyl‐ether‐β‐CD with a degree of substitution of 6.5 and 10 at neutral pH proved to be the most suitable chiral selector for both compounds. Various dual CD systems were also compared, and the possible mechanisms of enantiomer separation were investigated. A dual selector system containing sulfobutyl‐ether‐β‐CD degree of substitution 6.5 and native γ‐CD proved to be the most adequate system for the separations. Method optimization was carried out using an experimental design approach, performing an initial fractional factorial screening design, followed by a central composite design to establish the optimal analytical conditions. The optimized methods (25 mM phosphate buffer, pH 7, 10 mM sulfobutyl‐ether‐β‐CD/20 mM γ‐CD, +20 kV voltage; 17°C temperature; 50 mbar/3 s injection, detection at 210 nm for lansoprazole; 25 mM phosphate buffer, pH 7, 15 mM sulfobutyl‐ether‐β‐CD/30 mM γ‐CD, +20 kV voltage; 18°C temperature; 50 mbar/3 s injection, detection at 210 nm for rabeprazole) provided baseline separation for lansoprazole (R_s = 2.91) and rabeprazole (R_s = 2.53) enantiomers with favorable migration order (in both cases the S‐enantiomers migrates first). The optimized methods were validated according to current guidelines and proved to be reliable, linear, precise, and accurate for the determination of 0.15% distomer as chiral impurity in dexlansoprazole and dexrabeprazole samples.     

Determination of brompheniramine enantiomers in rat plasma by cation‐selective exhaustive injection and sweeping cyclodextrin modified electrokinetic chromatography method

A method consisting of cation‐selective exhaustive injection and sweeping (CSEI‐sweeping) as online preconcentration followed by a cyclodextrin modified electrokinetic chromatography (CDEKC) enantioseparation has been developed for the simultaneous determination of two brompheniramine enantiomers in rat plasma. In this method, analytes were electrokinetically injected at a voltage of 8 kV for 80 s in a fused‐silica capillary. Prior to the injection, the capillary was rinsed with 50 mM phosphate buffer of pH 3.5, followed by a plug of a higher conductivity buffer (150 mM phosphate pH 3.5, 20 psi, 6 min) and a plug of water (0.5 psi, 5 s). Separation was carried out applying –20 kV in 50 mM phosphate buffer, pH 3.5, containing 10% v/v ACN and 30 mg/mL sulfated‐β‐cyclodextrin (S‐β‐CD). Analytical signals were monitored at 210 nm. The detection sensitivity of brompheniramine enantiomers was enhanced by about 2400‐fold compared to the normal injection mode (hydrodynamic injection for 3 s at 0.5 psi, with a BGE of 50 mM phosphate buffer containing 20 mg/mL S‐β‐CD at pH 3.5), and LLOQ of two enantiomers were both 0.0100 μg/mL. In addition, this method had fairly good repeatability and showed promising capabilities in the application of stereoselective pharmacokinetic investigations for brompheniramine enantiomers in rat.     

Enantiomeric separation of R,S‐tolterodine and R,S‐methoxytolterodine with negatively charged cyclodextrins by capillary electrophoresis

The methods for separation of R,S‐tolterodine and R,S‐methoxytolterodine enantiomers using sulfated α‐, β‐CD and phosphated‐γ‐CD by CE in acidic BGE based on Tris/phosphate pH 2.5 buffer were developed. Sulfated α‐ and β‐CD allow anodic detection while phosphated‐γ‐CD allows only cathodic detection of the separated enantiomers. The influence of chiral selector (CS)'s concentration as well as the influence of composition and concentration of BGE on resolutions were studied. Reversal migration order of tolterodine and methoxytolterodine enantiomers was observed, when sulfated‐α‐ and sulfated‐β‐CD were used. The developed methods with all three studied CSs, were validated and compared. All proposed methods enable determination of 0.2% of S‐tolterodine as an optical impurity in pills, however the method with phosphated‐γ‐CD provided lower detection limit, better repeatability of peak areas and migration times, and also lower consumption of CS. Developed method employing phosphated‐γ‐CD that was applied for the determination of optical purity of R‐tolterodine in commercial pills.     

Chiral separation of cathinone derivatives using β‐cyclodextrin‐assisted capillary electrophoresis–Comparison of four different β‐cyclodextrin derivatives used as chiral selectors

In the past decade, more than 100 different cathinone derivatives slopped over entire Europe due to their enormous popularity. Generally, these novel psychoactive substances are easily available via the internet. This fact leads to various social problems, since cathinones are substances with consciousness‐changing effects and are mainly misused for recreational matters by their consumers. Cathinones possess a chiral center including two enantiomeric forms with potentially different pharmacological behavior. This fact makes analytical method development regarding their chiral separation indispensable. In this study, a chiral capillary zone electrophoresis method for the enantioseparation of 61 cathinone and pyrovalerone derivatives was developed by means of four different β‐cyclodextrin derivatives. As chiral selectors, native β‐cyclodextrin as well as three of its derivatives namely acetyl‐β‐cyclodextrin, 2‐hydroxypropyl‐β‐cyclodextrin, and carboxymethyl‐β‐cyclodextrin were used. The cathinone and pyrovalerone derivatives were either purchased in internet stores or seized by police. As a result, overall 58 of 61 studied substances were partially or baseline separated by at least one of the four chiral selectors using 10 mM of β‐cyclodextrin derivative in a 10 mM sodium phosphate buffer (pH 2.5). Furthermore, the method was found to be suitable for simultaneous enantioseparations, for enantiomeric purity checks and to differentiate between positional isomers. Moreover, an intra‐ and an interday validation was performed successfully for each chiral selector to prove the robustness of the method.     

Enantioseparation of chiral benzimidazole derivatives by electrokinetic chromatography using sulfated cyclodextrins

Baseline separation of 18 new substituted benzimidazole derivatives, potent AMP‐activated protein kinase (AMPK) activators, with one chiral center, was achieved by CD‐EKC using sulfated and highly sulfated CDs (SCDs and HS‐CDs) as chiral selectors. The influence of the type and concentration of the chiral selectors on the enantioseparations was investigated. The SCDs exhibit a very high enantioselectivity power since they allow excellent enantiomeric resolutions compared to those obtained with the neutral CDs. The enantiomers were resolved with analysis times around 6 min using 25 mM phosphate buffer at pH 2.5 containing either β‐S‐CD, HS‐β‐CD, HS‐γ‐CD (3 or 4% w/v) at 25°C, with a voltage of 20 kV. The apparent association constants of the inclusion complexes were calculated. The study of the solute structure‐enantioseparation relationships seems to show the high contribution of the interactions between the solutes phenyl ring and the CDs to the enantiorecognition process. The optimized method was briefly validated (LOD less than 1%) and the purity of enantiomers of compound 3 was determined. The enantiomer migration shows reversal order depending on the kind of CD.     

Separation and Determination of Cold Medicine Ingredients by Capillary Zone Electrophoresis Using Sulfated β‐Cyclodextrin as an Electrolyte Modifier and Chiral Selector

Capillary zone electrophoretic separations of cold medicine ingredients, including acetaminophen (AC), dextromethorphan (DMF) and racemates of phenylpropanolamine (PPA) and chlorpheniramine maleate (CPM) using randomly sulfated‐β‐CD (S‐β‐CD) as an electrolyte modifier and a chiral selector were investigated. The results indicate that S‐β‐CD is an excellent chiral selector and a suitable electrolyte modifier as well for the separation of those cold medicine ingredients. Influences of S‐β‐CD concentration and buffer concentration on the separation were examined. Baseline separation of these cold medicine ingredients with 1.0 % (w/v) S‐β‐CD could be simultaneously and successfully achieved within 11.8 minutes. In addition, S‐β‐CD could also act as a chiral selector for enantioseparation of PPA and CPM. A high enantioselectivity was obtained for these two analytes. Linear relationships between the peak area and its concentration for the calibration curves of AC and DMF were obtained (correlation coefficients: 0.9987 for AC, 0.9965 for DMF, respectively). The relative standard deviations of the migration time and peak area of AC and DMF were 0.19, 2.44 % and 0.34, 2.99 %, respectively. Detection limits were 0.93 and 2.57 μg/mL for AC and DMF, respectively. Recoveries of AC and DMF ranging between 102.42 and 97.28 % were observed. The proposed method was successfully applied to the determination of AC and DMF in cold medicines.     

Enantiomeric separation of amlodipine and its two chiral impurities by nano‐liquid chromatography and capillary electrochromatography using a chiral stationary phase based on cellulose tris(4‐chloro‐3‐methylphenylcarbamate)

In this work, a novel polysaccharide‐based chiral stationary phase, cellulose tris(4‐chloro‐3‐methylphenylcarbamate), also called Sepapak 4 has been evaluated for the chiral separation of amlodipine (AML) and its two impurities. AML is a powerful vasodilatator drug used for the treatment of hypertension. Capillary columns of 100 μm id packed with the chiral stationary phase were used for both nano‐LC and CEC experiments. The optimization of the mobile phase composed of ACN/water, (90:10, v/v) containing 15 mM ammonium borate pH 10.0 in nano‐LC allowed the chiral separation of AML and the two impurities, but not in a single run. With the purpose to obtain the separation of the three pairs of enantiomers simultaneously, CEC analyses were performed in the same conditions achieving better enantioresolution and higher separation efficiencies for each compound. To fully resolve the mixture of six enantiomers, parameters such as buffer pH and concentration sample injection have been then investigated. A mixture of ACN/water (90:10, v/v) containing 5 mM ammonium borate buffer pH 9.0 enabled the complete separation of the three couples of enantiomers in less than 30 min. The optimized CEC method was therefore validated and applied to the analysis of pharmaceutical formulation declared to contain only AML racemate.     

Enantioseparation of esbiothrin by cyclodextrin‐modified microemulsion and micellar electrokinetic chromatography

A comparison between chiral cyclodextrin‐modified microemulsion electrokinetic chromatography (CD‐MEEKC) and cyclodextrin‐modified micellar electrokinetic chromatography (CD‐MEKC) for the enantiomeric separation of esbiothrin was carried out. For both methods, the separation conditions were optimized by varying CD types and concentration, running buffer pH and compositions, organic modifiers, and temperature. The optimal CD‐MEEKC conditions were 0.8% n‐heptane, 2.3% SDS, 6.6% n‐butanol, 90.3% 10 mM sodium tetraborate containing 3% (w/v, the ratio of CD mass to microemulsion volume) methyl‐β‐cyclodextrin, pH 10, 25°C. The optimized CD‐MEKC conditions were 3.3% SDS, 96.7% 10 mM sodium tetraborate containing 5% (w/v) β‐CD, pH 10, 25°C. The difference in physicochemical properties of the buffer and CDs resulted in different optimal CD type. The competitive distribution between the microemulsion (or micelle) and chiral CD contributed to the chiral separation. Both methods provided excellent separation (R_s ～? 3) with similar migration time (ca. 15 min). CD‐MEEKC provided higher separation efficiencies (>300000) than CD‐MEKC (>200000). The LODs for CD‐MEEKC and CD‐MEKC were 4.7 μg/mL and 3.2 μg/mL, respectively. The RSDs of migration time and peak area for CD‐MEEKC were slightly higher than for CD‐MEKC. Both the demonstrated CD‐MEEKC and CD‐MEKC methods provided high efficiencies, low LODs, and reproducible enantioseparations of esbiothrin.     

Capillary electrophoretic enantioseparation of m‐nisoldipine using two different β‐cyclodextrins

The methods for the enantioseparation of m‐nisoldipine, a new 1,4‐dihydropyridine calcium ion antagonist, were developed. The elaborated methods of m‐nisoldipine enantiomers separation were successfully performed using an anionic CD–sulfobutyl ether‐β‐CD (SBE‐β‐CD) or carboxymethyl‐β‐CD as chiral selector. However, the results indicated that SBE‐β‐CD was a better chiral selector for enantioseparation of the neutral m‐nisoldipine. Furthermore, comparing the two SBE‐β‐CDs, the derivative with a higher degree of substitution (DS) of 7.0 induced better enantioresolution than the one with low DS (4.0). In addition, possible chiral recognition mechanisms of dihydropyridines were discussed.     

Combined use of ionic liquid and sulfobutylether‐β‐cyclodextrin as electrolyte additives for separation and determination of camptothecin alkaloids by CZE

This work reported that ionic liquid (IL) ([Bmim] [PF₆]) and sulfobutylether‐β‐CD (SBE‐β‐CD) were used as electrolyte additives for the separation and determination of camptothecin (CPT) alkaloids by CZE. Separation parameters such as the buffer type, pH, and concentration of the running buffer, the concentration of SBE‐β‐CD and IL, temperature, and separation voltage were all investigated in order to achieve the maximum possible resolution. The four analytes were baseline separated within 10 min in capillary at the separation voltage of 15 kV with a running buffer consisting of 20 mM borate buffer, 20 mM IL, and 100 mM SBE‐β‐CD at pH 9.0. Under such conditions, good linearity about two orders of magnitudes of peak areas was achieved for the investigated CPT alkaloids with the correlation coefficients ranging from 0.9946 to 0.9985. For all analytes, detection limits (S/N = 3) and quantitation limits (S/N = 10) range from 0.05 to 0.92 μg/mL and 0.17 to 3.06 μg/mL, respectively. The proposed method has not only been successfully applied to the separation and determination of CPT alkaloids but also showed that IL seemed to be a promising additive in CZE separation.     

Separation and Migration Behavior of Dichlorophenols in β‐Cyclodextrin‐Modified Capillary Zone Electrophoresis

The separation and migration behavior of six isomeric dichlorophenols (DCPs) in cyclodextrin‐modified capillary zone electrophoresis (CD‐CZE) using a phosphate‐borate buffer at alkaline pH with β‐CD and hydroxypropyl‐β‐CD (HP‐β‐CD) as electrolyte modifiers were investigated. The influence of buffer pH and the concentration of β‐cyclodextrins were examined. The results indicate that baseline separation of six isomeric DCPs can be achieved with addition of β‐CD concentration in the range of 2.0‐10 mM or HP‐β‐CD concentration in the range of 4.0‐10 mM at pH 10.0. Binding constants of DCPs to β‐CDs were evaluated for a better understanding of the interaction of DCPs with β‐CDs.     

Enantioseparation of acetyltropic acid by countercurrent chromatography with sulfobutyl ether‐β‐cyclodextrin as chiral selector

Acetyltropic acid is an important synthetic intermediate for preparation of tropane alkaloid derivatives, which can be used as anticholinergic drugs, deliriants, and stimulants. In the present work, acetyltropic acid was successfully enantioseparated by countercurrent chromatography using sulfobutyl ether‐β‐cyclodextrin as chiral selector. A biphasic solvent system composed of n‐butyl acetate/n‐hexane/0.1 mol/L citrate buffer at pH = 2.2 containing 0.1 mol/L of sulfobutyl ether‐β‐cyclodextrin (7:3:10, v/v) was selected, which produced a suitable distribution ratio D_S = 1.14, D_R = 2.31 and a high enantioseparation factor α = 2.03. Baseline separation was achieved for preparative enantioseparation of 50 mg of racemic acetyltropic acid. A method for chiral analysis of acetyltropic acid by conventional reverse phase liquid chromatography with hydroxylpropyl‐β‐cyclodextrin as mobile phase additive was established, and formation constants of inclusion complex were determined. It was found that different substituted β‐cyclodextrin should be selected for enantioseparation of acetyltropic acid by countercurrent chromatography and reverse phase liquid chromatography.