西他沙星差向异构体的毛细管电泳分离

以γ-环糊精和D-苯丙氨酸为手性选择剂,采用毛细管区带电泳成功地分离了新型抗菌素西他沙星差向异构体。考察了添加剂的种类、浓度和缓冲溶液的pH对毛细管电泳分离西他沙星的影响。分离电压为15 kV,选用60 cm(有效长度52.5 cm)×50 μm i.d.的石英毛细管,缓冲溶液组成为10 mmol/L KH2PO4-K2HPO4(pH 4.5),10 mmol/L CuSO4,20 mmol/L γ-环糊精和 10 mmol/L D-苯丙氨酸。实验结果表明,添加剂的种类和浓度是影响西他沙星手性分离的重要因素,只有当 D-苯丙氨酸、铜离子和γ-环糊精同时存在并达到一定浓度时,西他沙星差向异构体在毛细管电泳中才具有良好的分离效果。该方法可用于西他沙星差向异构体的定量分析。     

Complementary on-line preconcentration strategies for steroids by capillary electrophoresis

Complementary on-line preconcentration strategies are needed when analyzing different classes of solutes in real samples by capillary electrophoresis (CE) with UV detection. The performance of three different on-line preconcentration (focusing) techniques under alkaline conditions was examined in terms of their selectivity and sensitivity enhancement for a group of steroids, including classes of androgens, corticosteroids and estrogens. Electrokinetic focusing of large sample injection plugs (up to 28% of effective capillary length or 22.1 cm) directly on-capillary can be tuned for specific classes of steroids based on changes in their mobility (velocity) using a multi-section electrolyte system in CE. A dynamic pH junction was applied for the selective resolution and focusing of weakly acidic estrogens using borate, pH 11.0 and pH 8.0 in the background electrolyte and the sample, respectively. Sweeping, using an anionic bile acid surfactant and neutral gamma-cyclodextrin (gamma-CD) under alkaline conditions (pH 8), resulted in focusing and separation of the moderately hydrophobic (non-ionic) classes of steroids, such as androgen and corticosteroids. Optimal focusing and resolution of all test steroids under a single buffer condition was realized by a dynamic pH junction-sweeping format using borate, pH 11.0 and bile acid surfactant with gamma-CD in the BGE, whereas the sample is devoid of surfactant at pH 8.0. The design of selective on-line focusing strategies in CE is highlighted by the analysis of microgram amounts of ethynyl estradiol derived from a female contraceptive pill extract using the dynamic pH junction method, which resulted in over a 100-fold enhancement in concentration sensitivity.     

Enantioseparation of binaphthol and its mono derivatives by cyclodextrin-modified capillary zone electrophoresis

Chiral binaphthols belong to the group of most effective ligands for asymmetrical catalysis. In this context, various binaphthols presenting original substituents have been synthesized. Their study through capillary electrophoresis is the object of this work. The literature dedicated to the separation of atropisomers by capillary electrophoresis, corresponding only to binaphthol, reveals that its enantioseparation is always delicate because of the influence of many factors and the resolutions obtained are weak. Therefore, for a structured optimization, we first successfully evaluated the acidity constants of different binaphthols by means of capillary electrophoresis. With these known physicochemical characteristics, we could successfully carry out enantiomeric separations of the different binaphthols at pH 11.5, practically in completely ionized form, in phosphate medium, and in the presence of cyclodextrin (CD), with analysis times lower than 8min. The nature of CDs (alpha-CD, beta-CD, gamma-CD, hydroxypropyl-alpha-cyclodextrin (HP-alpha-CD), HP-beta-CD, HP-gamma-CD and trimethyl-beta-CD (TM-beta-CD)) and other factors in relation to enantiomeric resolution (applied voltage, nature and concentration of the electrolyte, and concentration of cyclodextrin) were optimized. These studies allowed us to determine the optimal conditions of separation (concentration and nature of CD) for each of the studied binaphthols. It is necessary to mention that, for the 1,1'-binaphthyl-2,2'-diol (Binol) at pH 11.5, the S atropisomer always migrated first, regardless of the nature and concentration of the cyclodextrin used. Moreover, an inversion in elution order of the two atropisomers as a function of pH was observed with gamma-CD (pH range: 10-11.5). The R atropisomer migrated first at pH 10. At pH 10.8 the migration order of the two atropisomers of Binol was reversed as a function of gamma-CD concentration. Finally, the addition of chiral ionic liquids (R(-)-1-hydroxy-N,N,N-trimethylbutan-2-aminium bis(trifluoromethylsulfonyl)imide and S(+)-tetrabutylammonium camphorsulfonate) was conducted. In the case of S(+)-tetrabutylammonium camphorsulfonate, a weak antagonistic effect was observed with modeling the evolution of enantiomeric resolution by means of the experimental design, while in the case of R(-)-1-hydroxy-N,N,N-trimethylbutan-2-aminium bis(trifluoromethylsulfonyl)imide the effect was neutral.     

Separation of monomethyl-benz[a]anthracene isomers using cyclodextrin-modified electrokinetic chromatography

Cyclodextrin-modified electrokinetic chromatography (CD-EKC) was investigated for the separation of 12 monomethylbenz[a]anthracene (MBA) isomers. Combined use of a polymeric surfactant, poly(sodium 10-undecenyl sulfate) (poly-SUS), with various types of neutral cyclodextrins (CDs) [beta-CD, gamma-CD, dimethyl-beta-CD (DM-beta-CD), trimethyl-beta-CD (TM-beta-CD) and hydroxypropyl-beta-CD (HP-beta-CD)] were successful in CD-EKC separation of the MBA isomers. Baseline resolution of 10 of the 12 isomers, except for 9-MBA and 2-MBA, was achieved with gamma-CD at pH 9.75. The beta-CD, gamma-CD, and beta-CD derivatives (DM-beta-CD, TM-beta-CD, HP-beta-CD) were found to have different resolution and selectivity. Additionally, the tR/t0 values of isomers were found to be dependent on the type and concentration of the CD additives. In general, tR/t0 values of MBA isomers decrease with an increase in the concentration of beta-CD derivatives, whereas the reversed was true when the concentrations of native beta-CD and gamma-CD were varied. The combination of 5 mM gamma-CD, 0.5% (w/v) poly-SUS, 35% (v/v) acetonitrile at a pH of 9.75 provided the best selectivity and resolution of the MBA isomers with a separation time of 110 min. However, the use of 30 mM DM-beta-CD under similar EKC conditions resulted in much faster separation (ca. 16 min) of 10 MBA isomers.     

Laser-induced fluorescence detection at 266 nm in capillary electrophoresis. Polycyclic aromatic hydrocarbon metabolites in biota

The separation of five phenolic polycyclic aromatic hydrocarbon metabolites (hydroxy-PAHs) has been performed by cyclodextrin-modified micellar electrokinetic chromatography (CD-MEKC) using a 30 mM borate buffer (pH 9.0) containing 60 mM sodium dodecyl sulfate and varying concentrations of gamma-cyclodextrin (gamma-CD). A concentration of 12.5 mM gamma-CD was found to provide a baseline separation of the five hydroxy-PAHs. We applied conventional fluorescence and laser-induced fluorescence (LIF) detection, using a new, small-size, quadrupled Nd-YAG laser emitting at 266 nm. The best limits of detection, in the low ng/ml range, were achieved using LIF detection. For all analytes, linearity was observed up to ca. 100 ng/ml. As an application, conjugated pyrene metabolites in hepatopancreas samples from the terrestrial isopods Oniscus asellus and Porcellio scaber were separated and detected. Finally, flatfish bile samples from individuals exposed to polluted sediment or crude oil, which were part of an interlaboratory study, were analyzed by CD-MEKC with conventional fluorescence and LIF detection to determine the 1-hydroxypyrene concentrations.     

Enantioseparation of phenothiazines in cyclodextrin-modified capillary zone electrophoresis: reversal of migration order

Enantioseparations of phenothiazines with gamma-cyclodextrin (gamma-CD) as a chiral selector were investigated using citrate and phosphate buffer electrolytes at pH 3.0. Reversal of the enantiomer migration order of promethazine, ethopropazine, and trimeprazine was observed by varying gamma-CD concentration in the range of 5-9 mM, 2.5-4.5 mM and 1.5-2.8 mM, respectively, using 100 mM citrate buffer at pH 3.0. As in the case of beta-CD, the (+)-enantiomers of phenothiazines possess greater binding strength to gamma-CD than the (-)-enantiomers. The evaluation of the binding constants and limiting mobility of the complexes formed between the enantiomers of phenothiazines and gamma-CD reveals that the binding strength of phenothiazines to gamma-CD and the differences in the binding constants and limiting mobility of the complexes are responsible for the enantiomer migration reversal. Both the binding constants and limiting mobility of the complexes between the (+)-enantiomers of phenothiazine and gamma-CD are greater than those of the corresponding (-)-enantiomers in a citrate buffer, while the binding constants of the complexes primarily determined the migration order of the enantiomers in a phosphate buffer. Compared with the results obtained using a phosphate buffer, we may conclude that citrate buffer which involves competitive complexation with chiral selector plays a significant role in the enantiomer migration reversal.     

Enantioseparation of chiral thiobarbiturates using cyclodextrin-modified capillary electrophoresis

The racemates of several chiral thiobarbiturates were separated by using different cyclodextrins in capillary electrophoresis (CE). Six neutral and negatively charged cyclodextrins 1 (CDs) were employed as chiral separators whereof five led to successful separation of enantiomeric thiobarbiturate pairs. The CDs used were the native alpha-CD, beta-CD, gamma-CD, and heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (HDM) as well as heptakis-(2,3-di-O-methyl-6-sulfato)-beta-cyclodextrin (HDMS) and heptakis-(2,3-di-O-acetyl-6-sulfato)-beta-CD (HDAS). Five of the six chiral thiobarbiturates studied could be resolved at a basic pH value of 9.4 and a phosphate buffer concentration of 100 mM in a fused-silica capillary. Structurally related substances showed a similar behavior in separation: 1 and 2 bearing the center of chirality in the side chain at C5 can be best separated using gamma-CD, the N-alkyl-substituted compounds 3 and 4 as well as the N/S-dialkyl-substituted compound 5 could be resolved with HDM. Using the neutral CDs, the migration times were relatively small (< 11 min). 3 and 4 could be also resolved by means of the negatively charged HDMS. In the latter case, the migration time is twice as long as with HDM.     

Investigation on gamma-cyclodextrin nanotube induced by N,N'-diphenylbenzidine molecule

Dynamic light scattering (DLS) measurement provides an effective way to investigate the formation of nanotube of gamma-cyclodextrin (gamma-CD) induced by N,N'-diphenylbenzidine (DPB) in water. With the combination of steady-state fluorescence and fluorescence anisotropy experiments, it was found that for alpha- and beta-CD, only 1:2 (guest:host) inclusion complexes were formed and for gamma-CD, cyclodextrin nanotube was formed involving 16 gamma-CD units at maximum. The pH effect studies with both DLS and fluorescence anisotropy measurements indicated that the hydrogen bonding between neighboring CDs was necessary to the formation of cyclodextrin nanotube. In the temperature experiment, we found that the nanotube of DPB-gamma-CD could exist stably at relatively high temperatures and the transition point for structural collapse was estimated to be around 54 degrees C. The aggregation states of both gamma-CD itself and DPB-gamma-CD nanotube were observed with TEM.     

Nonaqueous and aqueous-organic media for the enantiomeric separations of neutral organophosphorus pesticides by CE

The enantiomeric separation of some poorly water-soluble organophosphorus pesticides (OPs) has been investigated using nonaqueous solvent and aqueous-organic solvent systems. In this work, sodium cholate (SC) either with SDS or gamma-CD was used to achieve enantiomeric separations of four neutral and poorly water-soluble OPs, i.e., profenofos, prothiofos, sulprofos, and pyraclofos. Electrophoretic medium consisted of a mixture of methanol (MeOH) with ACN (4:1 v/v) or a mixture of MeOH with H(2)O and ACN (5:4:1 v/v/v). On one hand, NACE was applied for enantiomeric separation of pyraclofos using a large amount of chiral and achiral surfactants (SC and SDS). On the other hand, H(2)O was added to act as a solvent additive to increase the solubility of gamma-CD in the organic solvents such as MeOH and ACN, in which the solubility of gamma-CD was very low. The presence of H(2)O was found to be particularly useful for the enantiomeric separation of profenofos, prothiofos, and sulprofos. In this way, the range of application of the neutral CDs in CE has been extended. In addition, SC was used as the only electrolyte. The proposed method has been applied for the analysis of soil samples.     

Chiral separability of hydrophobic boron cluster anions with native cyclodextrins in water-methanol background electrolytes

Cluster anions of boron are built up on three-center two-electron bonds in contrast to naturally occurring compounds and their synthetic analogs. Methanol works as a solvent and as a competing agent, which advantageously adjusts reasonable strength of their interaction with native CDs in water-organic BGE. The highest methanol concentration preserving chiral discrimination of atropoisomers of individual anions is approximately 35, 55 and 75% v/v for alpha-, beta- and gamma-CD, respectively. alpha-CD separates anionic 7, 8-nido-dicarbaundecaborate clusters with small exo-skeletal substituents. beta-CD separates anions of all four tested structural types. The efficiency of separation of a compound with alpha- or beta-CD is always markedly lower than the separation efficiency at the absence of a CD in BGE. The efficiency of separation of a compound with beta-CD is always lower than the efficiency of separation of the compound with alpha-CD. gamma-CD was proved to be unsuitable as a chiral selector because in BGEs with gamma-CD, effective mobilities of analytes as well as their differences continuously decrease. The decrease was ascribed to the decomposition of the gamma-CD. The assessment of analytical prospect of alpha- and beta-CDs as chiral selectors for chiral separations of boron cluster anions requires knowledge of stability of individual CDs at the conditions of analyses and recognition of the chance to eliminate low separation efficiency.     

Separation of some chiral flavanones by micellar electrokinetic chromatography

Micellar electrokinetic chromatography (MEKC) was applied for enantioseparation of selected flavanones, including naringin, hesperidin, neohesperidin, naringenin, hesperetin, pinostrobin, isosakuranetin, eriodictyol, and homoeriodictyol. gamma-Cyclodextrin (gamma-CD) and sodium cholate (SCh) were used as chiral modifiers inducing enantioselectivity to the background electrolyte. From among many investigated selectors only these two appeared to possess the best enantioselective properties in respect to studied flavanones. The mechanisms of their action are a little different; SCh used above critical micelle point concentration forms chiral micelles itself while gamma-CD is deprived of this property and requires addition of surfactants as, e.g., sodium dodecyl sulfate. It was found that SCh enables separation of flavanone glycosides diastereomers while separation of enantiomers of flavanone aglycones may be achieved with gamma-CD. Consideration of structural relation led to the suggestion that interaction of sugar moiety of glycosides with SCh micelles give rise to chiral recognition. MEKC appeared to be a suitable and efficient analytical tool to follow enantiomeric composition of flavanones.     

Cyclodextrin-modified monolithic columns for resolving dansyl amino acid enantiomers and positional isomers by capillary electrochromatography

We describe beta- and gamma-cyclodextrins (beta- and gamma-CD)-modified monolithic columns prepared by sol-gel process and chemical modifications. The monolithic silica column was fabricated inside a fused-silica capillary with 100 microm inner diameter by sol-gel process. The monolithic silica matrix was chemically modified chiral selectors of beta- or gamma-CDs with a spacer of 3-glycidoxypropyltrimethoxysilane by on-column reactions. Gamma-CD-modified monolithic column has successfully been applied for the separation of dansyl amino acid enantiomers. Beta-CD-modified monolithic column has been used for the separation of the positional isomers of o-, m-, and p-cresols and the enantioseparation of racemates of benzoin and several dansyl amino acids by capillary electrochromatography, respectively. For the separation of neutral positional isomers, a positive electric field was applied. However, for the separation of negatively charged analytes, a negative electric field was applied at the inlet of column. The separation efficiency of 5.0 x 10(4) theoretical plates/m for dansyl-L-threonine was obtained at electric field strength of -300 V/cm in the mobile phase of 50 mM 2-(N-morpholino)ethanesulfonic acid (MES)-Tris/methanol (70/30) buffer at pH 7.0. L-enantiomers were eluted as the first peak. Scanning electron micrograph showed that monolithic columns have the morphology of continuous skeleton and large through-pores.     

Determination of pharmaceuticals classified as emerging pollutants using capillary electrophoresis with capacitively coupled contactless conductivity detection

A study on the simultaneous separation of 13 pharmaceutical products by capillary electrophoresis with capacitively coupled contactless conductivity detection was presented. The parameters of the background electrolyte, such as pH, organic additives as well as types and concentrations of cyclodextrins (CD) were studied. The optimal separation conditions were achieved with a background electrolyte consisting of 9 mM Tris/5 mM lactic acid at pH 8.0, containing 5% n-propanol, 0.025% gamma-CD, 0.075% hydroxyl-beta-CD and 0.15% dimethyl-beta-CD. Limits of detections ranged from 61 to 1676 microg/L (S/N=3) and the relative standard deviations for migration time and peak area were below 2 and 6%, respectively. This demonstrated the potential of the capillary electrophoresis-capacitively coupled contactless conductivity detection method for biomedical and environmental analysis, as shown in the determination of pharmaceuticals identified as emerging pollutants in water samples.     

Separation of quaternary ammonium diastereomeric oligomers by capillary electrophoresis

The separation of novel diastereomeric trimers (3M) and pentamers (5M), derived from quaternary ammonium salts, was studied in conventional, uncoated and coated capillaries using capillary zone electrophoresis (CZE) with a variety of buffers and additives. Resolution of 5M diastereomers was best achieved using gamma-cyclodextrin (gamma-CD) as a chiral selector, while no diastereomeric resolution was realized for the 3M material.     

Inclusion complexes of Fe(III) tetrakis(4-sulfonatophenyl)porphyrin with cyclodextrins in aqueous solutions

In aqueous solutions, inclusion complexation of Fe(III) tetrakis(4-sulfonatophenyl)porphyrin (FeTSPP) with alpha-cyclodextrin (alpha-CD), beta-CD, gamma-CD, and heptakis(2,3,6-tri-O-methyl)-beta-CD (TM-beta-CD) has been examined by means of absorption and induced circular dichroism spectroscopy. FeTSPP has been found to form inclusion complexes with beta-CD, gamma-CD, and TM-beta-CD in pH 3.2 buffers. At pH 10.1, where FeTSPP self-associates to form an oxo-bridged dimer, FeTSPP also forms inclusion complexes with alpha-CD, beta-CD, gamma-CD, and TM-beta-CD. The stoichiometries of the CD-FeTSPP inclusion complexes are 1:1, except for TM-beta-CD in pH 10.1 buffers where its 1:1 inclusion complex associates with TM-beta-CD to form a 2:1 inclusion complex at high TM-beta-CD concentrations. Equilibrium constants of FeTSPP for the formation of the 1:1 inclusion complexes have been evaluated for beta-CD, gamma-CD, and TM-beta-CD. Induced circular dichroism spectra of FeTSPP in alpha-CD and beta-CD solutions exhibit a signal pattern (a negative sign) that is different from those in acidic and basic solutions containing gamma-CD and that in basic solution containing TM-beta-CD, suggesting different inclusion modes towards FeTSPP.     

胶束电动毛细管色谱法分离左旋十八甲基炔诺酮、睾酮和孕酮

胶束电动毛细管色谱法（MECC）被用于左施十八甲基炔诺酮（LNC）、睾酮（T）和孕酮（P）的分离。电泳缓冲液中含一定量的乙腈或甲醇等有机添加剂时,可以改善分离。当乙睛体积分数为0～15％时,样品的迁移时间tm随着乙腈体积分数的增加而增加,但当已腈体积分数大于15％时,样品的tm随乙腈体积分数的增加反而减少。如采用20mmol／L的2,6-二甲基-β-环糊精（DM-β-CD）作添加剂,不仅可提高分高度,而且能缩短分析时间,实现最佳分离。     

A new capillary zone electrophoresis method for the analysis of Ginkgo biloba extracts and Ginkgo biloba pharmaceutical products

Ginkgo biloba, traditional Chinese medicine is now generally accepted. Separation and determination of active components in G. biloba is important for the product quality control. Therefore, the development of an effective and reliable separation method is important. In this work, a new capillary electrophoretic (CZE) method for separation of the G. biloba leaf extracts components was developed and optimized by the use of experimental design and artificial neural network (ANN). Under best separation conditions, in gamma-CD-modified buffer, the separation was reached within 10 min (36 mM borate BGE, pH 9.2, 1 mM gamma-CD), while the hydrodynamic mode for sample injection (2 s) and UV detection at 270 nm were applied. The method developed was validated and applied for analysis of various extracts and G. biloba products.     

Separation and investigation of structure-mobility relationships of insect oostatic peptides by capillary zone electrophoresis

Capillary zone electrophoresis (CZE) has been applied to qualitative analysis, separation, and physicochemical characterization of synthetic insect oostatic peptides (IOPs) and their derivatives and fragments. Series of homologous IOPs were separated in three acidic background electrolytes (BGEs; pH 2.25, 2.30, 2.40) and an alkaline BGE (pH 8.1). Best separation was achieved in acid BGE composed of 100 mM H3PO4, 50 mM Tris, pH 2.25. The effective electrophoretic mobilities, mu(ep), of all IOPs in four BGEs were determined and several semiempirical models correlating effective mobility with charge-to-size ratio (mu(ep) versus q/Mr k) were tested to describe the migration behavior of IOP in CZE. None of models was found to be unambiguously applicable for the whole set of 20 IOPs differing in size (dipeptide - decapeptide) and charge (-2 to +0.77 elementary charges). However, a high coefficient of correlation, 0.9993, was found for the subset of homologous series of IOPs with decreasing number of proline residues at C-terminus, H-Tyr-Asp-Pro-Ala-Prox-OH, x = 6 - 0, for the dependence of mu(ep) on q/Mr k with k = 0.5 for IOPs as anions in alkaline BGE and with k = 2/3 for IOPs as cations in optimized acidic Tris-phosphate BGE. From these dependences the probable structure of IOPs in solution could be predicted.     

Separation of multicomponent mixtures of 2,4-dinitrophenyl labelled amino acids and their enantiomers by capillary zone electrophoresis

The use of capillary zone electrophoresis (CZE) for the separation of a group of 33 2,4-dinitrophenyl labeled amino acids (DNP-AA), including DNP-AA racemates, DNP-L-AA enantiomers and achiral DNP-AAs, was investigated. Alpha-, beta- and gamma-cyclodextrins (CDs) and their derivatives (hydroxypropyl derivatives of alpha-, beta- and gamma-CDs, polymeric beta-CD and 6A-methylamino-beta-cyclodextrin (MA-beta-CD)) served as complexing agents and chiral selectors in this investigation. Although native alpha- and gamma-CDs and their derivatives influenced the effective mobilities of the studied DNP-AAs in different ways, they generally failed to resolve enantiomers of the individual DNP-AAs. On the other hand, beta-CD and all of its derivatives were found to be effective in this respect. Of these, the best results were achieved with a positively charged MA-beta-CD and this chiral selector resolved enantiomers of ten DNP-AA racemates available for this study. However, a complete resolution of these enantiomers in one CZE run required that the effect of the chiral selector be complemented by complexing effects of polyvinyl pyrrolidone (PVP) or gamma-CD. Complexing and chiral recognition capabilities of MA-beta-CD combined with complexing effects of gamma-CD and PVP provided separating conditions suitable for the CZE separations of multicomponent mixtures of DNP-AAs with preserved resolutions of the enantiomers. For example, a mixture consisting of 43 DNP-AA constituents was resolved using an MA-beta-CD/gamma-CD combination with three peak overlaps.     

Development of a capillary zone electrophoresis method for the separation of a furan combinatorial library

Nine component mixtures of a furan library were simultaneously separated by capillary zone electrophoresis (CZE) using a phosphate buffer as a background electrolyte at low pH. The effects of buffer concentration, buffer pH, type and concentration of organic solvents on the electrophoretic mobility, resolution, and analysis time were systematically investigated. Resolution and efficiency of furan library components were further improved using cyclodextrin (CD)-modified CZE. Under optimum conditions, eight of the nine furans were baseline-resolved in less than 10 min at 30 kV using 50 mM phosphate buffer, 10% v/v acetonitrile (ACN), pH 2.0, with 5 mM gamma-CD.