Sample stacking in laboratory-on-a-chip devices

In this study, enantioseparations of five phenothiazines, including promethazine, ethopropazine, trimeprazine, methotrimeprazine, and thioridazine, in cyclodextrin (CD)-modified capillary zone electrophoresis were investigated using a phosphate buffer (40 mM) at pH 3.0. We focussed on the separation of phenothiazines with the use of CDs at low concentrations. Three different CDs, including β-CD, hydroxypropyl-β-CD (HP-β-CD) and γ-CD, were chosen as chiral selectors. The results indicate that effective enantioseparation of phenothiazines, except for methotrimeprazine, is simultaneously achievable with addition of γ-CD at a concentration of 2.5–6.0 mM. The enantiomers of ethopropazine and trimeprazine are effectively separated with addition of HP-β-CD at low concentrations, in the range 0.4–6.0 mM, whereas those of promethazine and trimeprazine are baseline resolved with β-CD at much lower concentrations (0.02–3.0 mM) than with HP-β-CD. The results also confirm that the separation window is greatly enlarged at low CD concentrations. Moreover, the drastic variations of the electrophoretic mobility of phenothiazines as a function of CD concentration reveal that phenothiazines interact very strongly with CDs in the order γ-CD相似文献   

Enatiomeric analysis of simendan by CE with beta-CD as chiral selector compared with CMPA-HPLC

The chiral separation of simendan enantiomers using capillary electrophoresis was studied with beta-cyclodextrin (beta-CD) as chiral selector. The influences of the concentration and pH of borate buffer solution, beta-CD concentration and methanol content in the background electrolyte were investigated. These factors were compared with those in an HPLC with beta-CD as chiral mobile phase additive (CMPA-HPLC). The quantification properties of the developed CE method were examined. A baseline separation of simendan enantiomers was achieved in the background electrolyte of 20 mmol/L borate buffer (pH 11.0) containing 12 mmol/L beta-CD-methanol (50:50 in volume ratio). The CE method is comparable with CMPA-HPLC in chiral resolution, although the optimal pH in CE (11.0) is much higher than that (6.0) in CMPA-HPLC. This chiral CE method is applicable to the quantitative ananlysis and enantiomeric excess value determination of L-simendan.     

Development of a capillary electrophoresis method for the enantioselective estimation of primaquine in pharmaceutical formulations

A capillary electrophoresis (CE) method has been developed that allows the separation and estimation of primaquine enantiomers using hydroxypropyl-gamma-cyclodextrin (HP-gamma -CD) as a chiral selector. The influence of chemical and instrumental parameters on the separation, such as type and concentration of CD, buffer concentration, buffer pH, applied voltage, capillary temperature, and injection time, were investigated. Good separation of the racemic mixture of primaquine was achieved using a fused-silica capillary (52.5 cm effective length x 50 microm id) and a background electrolyte composed of tris-phosphate buffer solution (50 mM, pH 2.5) containing 15 mM HP-gamma-CD as a chiral selector. The recommended applied voltage, capillary temperature, and injection time were 15 kV, 25 degrees C, and 6 s, respectively. Within-day and interday reproducibility of peak area and migration time gave relative standard deviation values ranging from 1.05-3.30%. Good recoveries (range of 96.8-104.9%) were obtained from the determination of placebos that were spiked with 0.25-1.00 mg/L primaquine. The proposed CE method was successfully applied to the assay of primaquine diphosphate in pharmaceutical formulations (tablets).     

Synthesis and application of a novel single-isomer mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β-cyclodextrin chloride as a chiral selector in capillary electrophoresis

A novel positively charged single-isomer of β-cyclodextrin, mono-6-deoxy-6-(3R,4R-dihydroxypyrrolidine)-β-CD chloride (dhypy-CDCl), was synthesized and employed as a chiral selector for the first time in capillary electrophoresis (CE) for the enantioseparation of anionic and ampholytic acids. The effects of the running buffer pH, chiral selector concentration, analyte structure and organic modifier on the enantioseparation were studied in detail. The chiral selectivity and resolution for most of the studied analytes decreased as the buffer pH increased in the range of 6.0–9.0. Increasing selector concentration led to decreased effective mobility, increased chiral selectivity and resolution for most of the studied analytes. Moreover, the hydroxyl groups located on the dihydroxypyrrolidine substituent of the dhypy-CDCl could have influence on the chiral separation.     

Preparation and enantiomer separation behavior of selectively methylated β-cyclodextrin-bonded stationary phases for high performance chromatography

Native and three selectively methylated β-cyclodextrin (β-CD)-bonded stationary phases without an unreacted spacer arm for liquid chromatography were prepared, where heptakis(2-O-methyl)-β-CD, heptakis(3-O-methyl)-β-CD and heptakis(2,3-di-O-methyl)-β-CD were used as the methylated β-CDs. The enantiomer separation abilities of the resulting β-CD stationary phases for 12 pairs of dansylamino acid enantiomers and six pairs of N-3,5-dinitrobenzoyl amino acid methyl esters as model solutes were investigated. The effects of pH and methanol content of the mobile phase on the retention and resolution were examined to optimize the mobile phase conditions. The optimum resolution for the dansylamino acids was achieved using a mobile phase consisting of 1.0% triethylammonium acetate buffer (pH 5.0)–methanol (v/v 4/6) on the β-CD stationary phase. Heptakis(3-O-methyl)- and heptakis(2,3-di-O-methyl)-β-CD-bonded stationary phases showed little enantiomer separation abilities for the dansylamino acids. The heptakis(2-O-methyl)-β-CD-bonded stationary phase exhibited no enantioselectivities for those solutes.

For the N-3,5-dinitrobenzoyl amino acid methyl esters, the optimum resolution was achieved using a mobile phase consisting of 1.0% triethylammonium acetate buffer (pH 5.0)–methanol (v/v 9/1) on a heptakis(2-O-methyl)-β-CD stationary phase. The heptakis(2,3-di-O-methyl)-β-CD-bonded stationary phases exhibited no enantioselectivities for the N-3,5-dinitrobenzoyl amino acid methyl esters. β-CD and heptakis(3-O-methyl)-β-CD-bonded stationary phases had no enantiomer separation abilities for those solutes except for the N-3,5-dinitrobenzoyl phenylalanine methyl ester.     

Enantioseparation of basic pharmaceutical compounds by capillary electrophoresis using sulfated cyclodextrins. Application to E-6006, a novel antidepressant

In this study, a chiral capillary electrophoresis method was optimized and validated for E-6006, a thienylpyrazolylethanamine derivative (pK_a 8.9). Enantioselectivity of neutral and anionic cyclodextrins (CDs) was evaluated at acid pH (3), obtaining cathodic and anodic migration, respectively. Hydroxypropyl-β-CD, carboxymethyl-β-CD and sulfobutyl ether-β-CD led to similar and partial selectivity, whereas sulfate (S)-β-CD produced baseline separation of the enantiomers. Four types of sulfated CDs were compared considering: cavity size (, β, γ) and random substitution versus unique derivative (S-β-CD, 6-heptakis-S-β-CD). Complete peak separation was obtained in all cases, but with different affinity and binding strength. Some factors that play a role in the complex formation include: position/region/degree of substitution, size of CD cavity and proportion of derivatives in mixtures. Enantioaffinity and enantioselectivity increased with the average of sulfate groups/mol. β Cavity size complexed better, although and γ cavities did not compromise separation. 6-Heptakis-S-β-CD had less affinity and separation efficiency, attributed to its lower degree and unique position of substitution. The method was optimized with S-β-CD (Aldrich, randomly substituted, 7–11 groups/mol). With this selector, the effect of pH value (3–9) was evaluated. Around pH 7 the cross-over point with change in the direction and order of migration was observed, associated with great enantioselectivity and long migration times. Fine tuning was done by adjusting the CD concentration and the buffer counterion. Definitive conditions were: uncoated silica capillary, 10 mM S-β-CD–25 mM sodium phosphate, pH 3. Validation parameters are included.     

Cyclodextrin-enhanced fluorescence and photochemically-induced fluorescence determination of five aromatic pesticides in water

The effect of β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) aqueous solutions upon the fluorescence and photochemically-induced fluorescence (PIF) properties of five pesticides, including coumatetralyl, pirimiphos-methyl, chlorpyriphos, deltamethrin and fenvalerate was investigated. A 1:1 stoichiometry was found for the β-CD and HP-β-CD complexes formed with all compounds. Binding constant values, ranging between about 90 and 830 M⁻¹ were calculated using the iterative nonlinear least-squares regression approach. Cyclodextrin-enhanced fluorescence and PIF methods were developed for the determination of these pesticides with linear dynamic ranges over two orders of magnitude, and limits of detection (LOD) between 0.2 and 54 ng ml⁻¹ according to the compound. Application to the analysis of tap water and river water samples yielded satisfactory recoveries (88–116%). The method seems to be suitable for environmental water analysis.     

毛细管区带电泳对手性药物盐酸美西律和盐酸异博定的对映体分离

应用环糊精-毛细管区带电泳体系对手性药物盐酸美西律和盐酸异博定的对映体分离进行了研究。结果表明, 在所研究的手性选择剂α-环糊精, β-环糊精, 二甲基-β-环糊精, 羟丙基β-环糊精和γ-环糊精中, 羟丙基β-环糊精对所研究的手性药物分离效果较好。对盐酸美西律和盐酸异博定的最佳羟丙基-β-环糊精浓度分别为30mmol/L和9mmol/L, 最佳缓冲溶液浓度为100mmol/L Tris-H3PO4(pH2.3)。向缓冲溶液中加入0.05%羟丙基纤维素(HPLC)可改善分离。盐酸美西律获得了接近基线的手性分离, 而盐酸异博定亦获得了较好的分离。     

On the use of dispersed nanoparticles modified with single layer beta-cyclodextrin as chiral selecor to enhance enantioseparation of clenbuterol with capillary electrophoresis

A new strategy for chiral separation by capillary electrophoresis employing modified-nanoparticles as chiral selector is described for clenbuterol analysis. Nanoparticles modified with β-cyclodextrin (β-CD) form a large surface area platform to serve as a pseudostationary chiral phase, which can be applied for the enhancement of the enantioseparation. The application of four kinds of nanoparticles was investigated (multi-walled nanotubes (MWNTs), polystyrene (PS), TiO₂ and Al₂O₃) modified with single layer β-CD as chiral selector in the enantioseparation of clenbuterol by capillary electrophoresis (CE). Successful clenbuterol enantioseparation could be achieved with the β-CD-modified MWNTs as chiral selector. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the β-CD modification of the nanoparticles. The effects of nanoparticles, surfactant, chiral selector (β-CD) and run buffer were studied in relation to the enantiomeric separation of clenbuterol. This study opens attractive perspectives for the use of modified nanoparticles for chiral separational purposes in CE.     

Separation of drug stereoisomers by capillary electrophoresis with cyclodextrins

Using capillary electrophoresis, the enantiomers and isomers of several chiral drug molecules were resolved with cyclodextrins. Parameters affecting the resolution between (+)- and (−)-epinephrine, such as pH, cyclodextrin concentration, buffer concentration, and capillary dimensions were investigated. In addition to this, the effect of cyclodextrin type (β and several derivatized β-cyclodextrins) on resolution between stereoisomers of several chiral drug was also investigated. This study showed that the structural features of the molecule, the derivative groups on the cyclodextrin, the buffer composition and the capillary dimensions influence resolution. The chiral drugs used in this study were propranolol, atenolol, betaxolol, dipivefrin, AL03152 (an aldose reductase inhibitor), AL03363 (an oxidation product of AL03152) and the cis/trans isomers of pilocarpine.     

Monosubstituted positively charged cyclodextrins: Synthesis and applications in chiral separation

Several series of novel structurally well-defined positively charged CDs, applicable to alpha-, beta- and gamma-CDs for chiral separation using CE and chromatographic techniques have been developed. The chiral resolution capabilities of different series CDs towards amino acids and anionic analytes in CE are systematically investigated by considering all separation parameters including CD type, alkyl chain length of the cations attached to the CD rim, CD concentration, buffer pH, separation temperature and organic solvent. Typical results are demonstrated in the context. Examples of chiral separation with HPLC and supercritical fluid chromatography are first demonstrated by using coated chiral stationary phases (CSPs). Optimum CD loading content on the coated CSPs was explored in the chiral separation of neutral analytes.     

Enantioseparation Of Aromatic Dipeptides Using Carboxymethyl-β-Cyclodextrin Polymer As Chiral Selector By Capillary Electrophoresis

ABSTRACT

Chiral separation of peptides is of interest because of the different biological activity of enantiomers. In this report, several underivatized dipeptides with benzene moieties were optically resolved by employing carboxymethyl-β-cyclodextrin polymer(CM-β-CD polymer) as chiral selector. The effects of different cyclodextrin types, selector concentration, buffer pH, and organic additive were examined. Selector concentration and buffer pH played significant roles in resolution. Enantioseparation was found to be negatively influenced by adding the organic additive into running buffer and even completely lost at the organic additive content of 16%. It was also noted that the dipeptides with short chain in the vicinity of the second chiral carbon atom showed better chiral resolution by using CM-β-CD polymer than by using either carboxyethyl-β-CD or succinylated-β-CD. Simultaneous chiral separation of a mixture of DL-Ala-DL-Phe and DL-Leu-DL-Phe was also obtained using 27 mg/ml CM-β-CD polymer in the running buffer at pH5.12.     

毛细管电泳法和高效液相色谱法拆分联萘二酚酸对映体

采用毛细管电泳法和高效液相色谱法直接拆分2,2′-二羟基-1,1′-联二萘-3,3′-二甲酸(HBNC)对映体.以四种不同的β-环糊精为手性添加剂,考察环糊精的种类与浓度、缓冲液pH值及浓度、分离电压、温度等因素对HBNC分离的影响.结果表明:采用10 mmol/L磺丁基醚-β-环糊精+20 mmol/L磷酸盐缓冲液(pH=7.0),20 kV分离电压,HBNC对映体在20 min内达到基线分离,分离度达到3.31.采用(S)-叔-亮氨酸基-(S)-1-(α-萘基)乙胺手性柱,正己烷-乙醇-三氟乙酸(97∶3∶0.2,V/V)流动相,HBNC对映体在40 min内也基本达到基线分离.     

新型三唑类抗真菌活性化合物毛细管电泳手性拆分及手性识别机理分子模拟研究

研究了7种新型三唑类抗真菌活性化合物的毛细管电泳法手性分离,利用计算机辅助分子模拟技术研究拆分机理。考察了8种中性环糊精手性添加剂,只有2,6-二甲基-β-环糊精对7种活性化合物都有手性识别能力。在30mmol/L NaH2PO4缓冲液中含2,6-二甲基-β-环糊精30mmol/L,用H3PO4调至pH 2.2,温度20℃,电压20kV,在此条件下7种活性化合物都能达到手性分离,其中4种活性化合物能达到基线分离(Rs>1.5)。应用计算机辅助分子模拟软件Discovery Studio 2.5/Sybyl/Gold模拟2,6-二甲基-β-环糊精与7种活性化合物主客体包结过程,并计算相互结合能,探讨手性识别机理,发现拆分结果与结合能的差异有关,结合能差异越大拆分结果越好。     

Effect of urea addition on chiral separation of dansylamino acids by capillary zone electrophoresis with cyclodextrins

The chiral separation ability of unmodified and di- and trimethylated -, β- and γ-cyclodextrins (CDs) as chiral selectors in capillary zone electrophoresis was investigated in the presence of urea derivatives using twelve dansylamino acids as model solutes. The addition of these urea derivatives (unsubstituted, methyl-, ethyl- and 1,3-dimethylureas) produced dramatic enhancement in the enantioselectivity of unmodified β-CD but also reduced the enantioselectivities of the other CDs.     

Enantiomeric resolution of chiral imidazole derivatives using capillary electrophoresis with cyclodextrin-type buffer modifiers

Enantiomeric resolutions of some chiral pharmaceuticals containing the imidazole (1,3-diazole) moiety were carried out using capillary electrophoresis. Various native cyclodextrins (ga-, β- and γ-cyclodextrin) and derivatized cyclodextrins (hydroxypropyl-, and sulfobutyl ether-β-cyclodextrin) were used as chiral buffer modifiers. The effects of the cavity size, the structure and the charge of the selectors on the chiral recognition ability were evaluated. The influence of the type and concentration of the organic modifier on the separation of miconazole enantiomers and the pH of the run buffer on the separation of enilconazole enantiomers was also studied.     

Enantiomeric Separation of β-Amino Alcohols by Capillary Electrophoresis Using DM-β-CD as Chiral Selector

Enantiomeric separations of several β-amino alcohol drugs, i.e., phenylephrine, epinephrine, norepinephrine, synephrine, and chlorprenaline were performed by capillary electrophoresis using DM-β-CD as a chiral selector. Five test solutes were baseline resolved in six minutes. The effects of DM-β-CD concentration, pH value, ionic strength of the buffer, and the type of β-CDs on resolution were investigated. The results indicated that DM-β-CD is suitable for enantiomeric separation of β-amino alcohols containing a phenyl group on the chiral atom. Enantiorecognition mechanisms for test solutes are also discussed.     

Enantiomeric separation of (R, S)-naproxen by recycling high speed counter-current chromatography with hydroxypropyl-β-cyclodextrin as chiral selector

Recycling high speed counter-current chromatography (HSCCC) was successfully applied to resolution of (R, S)-naproxen (NAP) using hydroxypropyl-β-cyclodextrin (HP-β-CD) as chiral selector. The two-phase solvent system composed of n-hexane-ethyl acetate-0.1 mol L(-1) phosphate buffer solution with pH=2.67 (8:2:10, v/v/v) was selected. Influence factors for the chiral separation process were investigated, including concentration of HP-β-CD, equilibrium temperature and pH of aqueous phase. Suitable elution mode was selected for HSCCC enantioseparation of (R, S)-NAP. Under optimum separation conditions, 29 mg of (R, S)-NAP was separated using preparative recycling HSCCC with the molar ratio HP-β-CD/NAP racemate 83:1. Technical details for recycling elution mode were discussed as for chiral HSCCC separation. The purities of both (S)-NAP and (R)-NAP were over 99.5% as determined by HPLC. Enantiomeric excess of (S)-NAP and (R)-NAP reached 99.4%. Recovery for NAP enantiomers from HSCCC fractions was 82-89%, yielding 13 mg of (S)-NAP and 12 mg of (R)-NAP.     

毛细管电泳法手性拆分4种氨酸和2种手性药物对映体

以双(6-氧-β-羧甲基-1,4-丁烯二酸单酯)-β-环糊精(DOCB-β-CD）作为手性添加剂,利用毛细管电泳对氨基酸和手性药物对映体进行拆分研究。 以20 mmol/L磷酸盐为缓冲溶液,考察了手性添加剂的浓度及缓冲溶液的pH值与分离电压等对拆分效果的影响,并在其优化条件下,实现了4种DL-氨基酸（苯丙氨酸、色氨酸、酪氨酸和组氨酸）以及手性药物（罗格列酮和酮洛芬）对映体的基线分离。     

Enantiospecific HPLC and CE Methods for Separation and Determination of S-Darifenacin in Pharmaceutical Formulations

Two separation techniques were developed for the determination of S-(−)darifenacin (DAR) in the presence of its R-(+) isomer: The first method is high performance liquid chromatography (HPLC) and the second is capillary electrophoresis (CE). Chiral separation for chromatographic HPLC method development was carried out for S-DAR on Daicel CROWNPAK CR (+) (5 μm, 4.0 × 150 mm) column which contains (3,3-diphenyl-1,1-binaphthyl)-crown-6 coated onto a 5.5 μm silica support. The mobile phase system was aqueous acidic 70 % HClO₄ (pH 2.5): methanol in the proportion of 90:10 v/v. This current mobile phase was delivered at flow rate 0.8 mL min⁻¹ using UV detector adjusted at 286 nm. In CE method, the enantiomers were separated using 50 μm inner diameter fused-silica capillary cut to total lengths of 31.2 cm using 50 mM phosphate buffer as background electrolyte adjusted to pH 2.5 by triethanolamine. A wide range of cyclodextrins (CDs) were used such as highly sulfated α, γ CDs, hydroxyl propyl-β-CD and sulfobutyl ether-β-CD as chiral selectors. The effects of chiral additives regarding its concentration and content of organic modifier on the enantioseparation were investigated. Linear concentration ranges were from 2.5 to 50 and 40 to 300 μg mL⁻¹ with detection limits 0.67 and 12.28 μg mL⁻¹ for chromatographic HPLC and electrophoretic CE methods, respectively. The two methods were validated according to ICH guidelines with respect to linearity, accuracy, precision, LOQ, LOD and robustness. The suggested methods are suitable for separation and quantitation of S-DAR in tablets.