Chiral separation of four fluoroquinolone compounds using capillary electrophoresis with hydroxypropyl-beta-cyclodextrin as chiral selector

A capillary zone electrophoresis (CZE) investigation on the enantiomeric separation of lomefloxacin, gatifloxacin, pazufloxacin and ofloxacin was undertaken. Resolution of the enantiomers was achieved using hydroxypropyl-beta-cyclodextrin (HP-beta-CD) as the chiral selector. Parameters influencing separation include cyclodextrin concentration, separational potential, pH and organic additive are discussed. A buffer consisting of 70 mM phosphate and 40 mM HP-beta-CD at pH 3.96 was found to be highly efficient for the separation of lomefloxacin, at pH 3.90 for gatifloxacin, at pH 5.04 for pazufloxacin and at pH 2.16 for ofloxacin. To the best of our knowledge, this is the first report on the enantiomeric resolution of lomefloxacin and gatifloxacin applying CE.     

Enantioselective separation of epoxides by capillary electrophoresis employing sulfated beta-cyclodextrin as chiral selector

A capillary electrophoresis method was developed for the enantioseparation of epoxide compounds. Sulfated beta-cyclodextrin was employed as a chiral selector. Phosphate-triethanolamine buffer showed a chiral separation effect when employing charged sulfated beta-cyclodextrin. The effect of pH, triethanolamine concentration and sulfated beta-cyclodextrin concentration on the resolution was studied. Methanol was tested as an organic modifier. Several other epoxides were successfully separated by the proposed method.     

Chiral separation of gemifloxacin in sodium-containing media using chiral crown ether as a chiral selector by capillary and microchip electrophoresis

Chiral crown ether, (+)-(18-crown-6)-tetracarboxylic acid (18C6H(4)), is an effective chiral selector for resolving enantiomeric primary amines owing to the difference in affinities between 18C6H(4) and each of the amine enantiomers. In addition to the destacking effect of sodium ion in the sample solution, the strong affinity of sodium ion to the polyether ring of crown ether is unfavorable to chiral capillary electrophoresis using 18C6H(4) as a chiral selector. In this report, the chiral separation of gemifloxacin dissolved in a saline sample matrix using 18C6H(4) was investigated. Adding a chelating agent, ethylenediaminetetraacetic acid (EDTA), to the run buffer greatly improved the separation efficiencies and peak shapes. The successful chiral separation of gemifloxacin in a urinary solution was demonstrated for both capillary and microchip electrophoresis.     

Chiral separation of amino acids by capillary electrophoresis with octyl-beta-thioglucopyranoside as chiral selector

In the present work, we propose the use of direct coupling of a headspace sampler to a mass spectrometer for the detection of adulterants in olive oil. Samples of olive oils were mixed with different proportions of sunflower oil and olive-pomace oil, respectively, and patterns of the volatile compounds in the original and mixed samples were generated. Application of the linear discriminant analysis technique to the data from the signals was sufficient to differentiate the adulterated from the non-adulterated oils and to discriminate the type of adulteration. The results obtained revealed 100% success in classification and close to 100% in prediction. The main advantages of the proposed methodology are the speed of analysis (since no prior sample preparation steps are required), low cost, and the simplicity of the measuring process.     

Optimization of the chiral resolution of baclofen by capillary electrophoresis using beta-cyclodextrin as the chiral selector

The chiral resolution of baclofen was achieved by capillary electrophoresis using a fused-silica capillary (60 cm x 75 microm ID). The background electrolyte (BGE) was phosphate buffer (pH 7.0, 50 mM)-acetonitrile (95:5 v/v) containing 10 mM beta-cyclodextrin. The applied voltage was 15 kV. The values of alpha and R(s) were 1.06 and 1.00, respectively. The electrophoretic conditions were optimized varying the pH and the ionic strength of the BGE, concentrations of beta-cyclodextrin and acetonitrile and the applied voltage.     

Enantiomeric separation by capillary electrophoresis using a crown ether as chiral selector.

This paper reviews chiral separations of primary amines by capillary electrophoresis and crown ether as chiral selector. Two possible mechanisms of chiral recognition by host-guest complexation are discussed: (i) The substituents of the crown ether act as barriers for the guest compounds, and (ii) lateral electrostatic interactions between host and guest occur. Experimental conditions affecting the separation are discussed in detail. A literature overview of practical applications is presented as well. More than 80 different primary amines were analyzed, whereupon the majority could be resolved using a screening method. It is shown that a synergistic effect on the resolution of chiral amines is observed when the chiral crown ether and cyclodextrins are simultaneously used in the same buffer system. This approach opens interesting perspectives for further method optimization.     

Enantioselective separation in capillary electrophoresis using a novel mono-6-propylammonium-β-cyclodextrin as chiral selector

The chiral resolving ability of a novel single-isomer cationic β-cyclodextrin (CD), mono-6^A-propylammonium-6^A-deoxy-β-cyclodextrin chloride (PrAMCD), as a chiral selector in capillary electrophoresis (CE) is reported in this work for the enantioseparation of hydroxy, carboxylic acids and amphoteric analytes. The effect of chiral selector concentration on the resolution was studied. Good resolutions were achieved for hydroxy acids. Optimum resolutions were obtained even at 3.5 mM CD concentration for carboxylic acids. The electrophoretic method showed good linearity and reproducibility in terms of migration times and peak areas, which should make it suitable for routine analysis. In addition, baseline chiral separation of a six-acid mixture was achieved within 20 min. PrAMCD proved to be an effective chiral selector for acidic analytes.     

Separation of basic drug enantiomers by capillary zone electrophoresis using glucuronyl glucosyl beta-cyclodextrin as a chiral selector.

Separations of basic drug enantiomers have been investigated using glucuronyl glucosyl beta-cyclodextrin (GUG beta-CD) as a chiral selector in the background electrolyte by capillary zone electrophoresis. The effects of GUG beta-CD concentration and running buffer pH on the migration times and resolution of 16 basic drug enantiomers were precisely examined using a linear polyacrylamide-coated capillary. High resolution of 16 basic drug enantiomers was generally attained with a running buffer pH 2.5 or 3.5 containing 10 mM GUG beta-CD. Next, we compared the chiral resolution abilities of GUG beta-CD with those of beta-CD and maltosyl beta-CD (G2 beta-CD). GUG beta-CD showed higher resolution for basic drug enantiomers tested than beta-CD and G2 beta-CD. This could be due to that hydrogen bonding or ionic interactions of uncharged and charged glucuronyl glucosyl groups of GUG beta-CD with an analyte could stabilize the inclusion complex.     

Azithromycin as a new chiral selector in capillary electrophoresis

In capillary electrophoresis (CE), separation of enantiomers of a chiral compound can be achieved through the chiral interactions and/or complex formation between the chiral selector and the enantiomeric analytes on leaving their diastereomeric forms with different stability constants and hence different mobilities. A great number of chiral selectors have been employed in CE and among them macrocyclic antibiotics exhibited excellent enantioselective properties towards a wide number of racemic compounds. The use of azithromycin (AZM) as a chiral selector has not been reported previously. This work reports the use of AZM as a chiral selector for the enantiomeric separations of five chiral drugs and one amino acid (tryptophan) in CE. The enantioseparation is carried out using polar organic mixtures of acetonitrile (ACN), methanol (MeOH), acetic acid and triethylamine as run buffer. The influences of the chiral selector concentration, ACN/MeOH ratio, applied voltage and capillary temperature on enantioseparation are investigated. The results show that AZM is a viable chiral selector in CE for the enantioseparation of the type of chiral drugs investigated.     

Chiral separation of bupivacaine enantiomers by capillary electrophoresis partial-filling technique with human serum albumin as chiral selector

Capillary electrophoresis (CE) is a powerful technique for enantiomer separations due to its intrinsic high separation efficiencies, speed of analysis, low reagent consumption and small sample requirements. However, some chiral selectors present strong background UV absorption providing high detection limits. The present paper deals with the application of the partial-filling technique to the separation of bupivacaine enantiomers by capillary electrophoresis using human serum albumin (HSA) as chiral selector. In this procedure the cationic surfactant cetyltrimethylammonium bromide (CTAB) was used as a dinamic capillary coating in order to reduce the electro-osmotic flow and detect both bupivacaine enantiomers out of the chiral selector plug. Several experimental conditions such as CTAB concentration, pH, HSA concentration and plug length, background electrolyte concentration, temperature and voltage were studied. Under the selected conditions it is possible to detect the separated enantiomers out of the HSA plug in less than 4 min using 50 mM Tris pH 8 as background electrolyte with 50 microM CTAB, at 30 degrees C and using a separation voltage of 25 kV. The proposed methodology was then validated for analytical purposes and applied to the analysis of pharmaceutical preparations commercially available. The results obtained with the proposed methodology were in good agreement with those declared by the manufacturers. The simplicity, sample throughput, accuracy, reproducibility and low cost of the proposed method make it suitable for the control of the enantiomeric composition of bupivacaine in pharmaceuticals.     

Infinite enantiomeric resolution of basic compounds using highly sulfated cyclodextrin as chiral selector in capillary electrophoresis

Four chiral basic analytes, namely methadone, fluoxetine, venlafaxine, and tramadol, were selected as model compounds for investigating their stereoselective separation with highly sulfated gamma-cyclodextrin (HS gamma-CD) by capillary electrophoresis (CE)-UV and CE-mass spectrometry (MS). At high concentration of chiral selector, the preferentially bonded enantiomer migrated faster in the anodic mode to the detector and high resolutions were obtained for all analytes. In the cathodic mode, at lower highly sulphated cyclodextrin (HS-CD) concentration, basic compounds could be detected, with the weakly bonded enantiomer migrating first (enantiomeric migration order inversion). It was also then possible, at intermediate HS-CD concentration, that only one enantiomer migrated to the detector as cation while the other enantiomer complexed with the CD was negatively charged and presented an opposite mobility. The latter never reached the detector achieving a perfect enantiomeric selectivity. Infinite chiral resolutions were thus achieved by CE-UV as well as by CE-electrospray ionisation (ESI)-MS where concentrations of HS-CD were adapted according to the negative contribution of the nebulization gas pressure of the interface.     

Application of dimethyl-beta-cyclodextrin as a chiral selector in capillary electrophoresis for enantiomer separation of ephedrine and related compounds in some drugs

Dimethyl-beta-cyclodextrin (DM-beta-CD) modified capillary electrophoresis has been developed for chiral separation of ephedrine and related compounds, such as (+/-)-norephedrine, (+/-)-N-methylephedrine, (+/-)-ephedrine and (+)-pseudoephedrine. The influence of some crucial parameters such as buffer concentration, pH value, DM-beta-CD concentration, applied voltage and separation temperature on the separation was investigated. Under the optimum conditions, i.e. 40 mM DM-beta-CD in 75 mM Tris (pH 2.5) as the running electrolyte, separation voltage +25 kV and temperature 25 degrees C, a satisfactory separation of the enantiomers was accomplished. The detection limits (S/N = 3) ranged from 65 to 161 ng/mL and the linear range was 0.15 to 101.0 microg/mL for pressure injection. The present method was successfully applied for the analysis of a series of drugs such as anti-tussive, the drug for rheum, the drug for rhinitis and a Chinese traditional herbal medicine, Ephedrae herba (Ma-Huang in Chinese). The recoveries of ephedrine and related compounds in real samples ranged from 97.6 to 103.5%. This method is useful in the simple and rapid analysis of ephedrine derivatives in marketed products.     

Investigation of enantiomeric separation of basic drugs by capillary electrophoresis using clindamycin phosphate as a novel chiral selector

A wide number of chiral selectors have been employed in CE and among them macrocyclic antibiotics exhibited excellent enantioselective properties toward plenteous racemic drugs. Different from macrocyclic antibiotics, the use of lincomycin antibiotics as chiral selectors has not been reported previously. In this study clindamycin phosphate belonging to the group of lincomycin antibiotics is first used as a novel chiral selector for the enantiomeric separations of several racemic basic drugs, which possess high separability, consisting of nefopam, citalopram, tryptophan, chlorphenamine and propranolol. Other basic drugs giving partial enantioseparation include tryptophan methyl ester, metoprolol and atenolol. Clindamycin phosphate possesses advantages such as high solubility and low viscosity in the water and very weak UV absorption. In the course of this work we observed that both migration time and enantioseparation were influenced by several parameters such as pH of the BGE, clindamycin concentration, capillary temperature, applied voltage and organic modifier. The optimum pH that was in the neutral or weak basic region but varied among drugs, a low capillary temperature and a clindamycin concentration of 60 or 80 mM are recommended as the optimum conditions for chiral separation of these drugs. Moreover, comparison of the influences of the studied parameters was further investigated by means of Statistical Product and Service Solutions in this paper.     

Chiral separation of hydroxyflavanones in cyclodextrin-modified capillary zone electrophoresis using sulfated cyclodextrins as chiral selectors

Chiral separations of three hydroxyflavanone aglycones, including 2'-, 3'-, and 4'-hydroxyflavanone, in capillary zone electrophoresis (CZE) using randomly sulfate-substituted beta-cyclodextrin (S-beta-CD) or dual cyclodextrin (CD) systems consisting of S-beta-CD and a neutral CD at low pH were investigated. The results indicate that S-beta-CD is an excellent chiral selector for enantioseparation of 2'-hydroxyflavanone and is a good chiral selector for 3'-hydroxyflavanone. Depending on the concentration of S-beta-CD ranging from 2.0 to 0.75% (w/v), the enantioresolution values were 10.5-19.5 and 1.8-3.4 for 2'- and 3'-hydroxyflavanone, respectively. The enantiomers of 4'-hydroxyflavanone could be effectively separated with S-beta-CD at a concentration of 2.0% (w/v) within 20 min. The enantioselectivity and enantioresolution follow the order 2'-hydroxyflavanone>3'-hydroxyflavanone>4'-hydroxyflavanone. Alternatively, with the addition of sodium dodecyl sulfate (SDS) monomers at low concentrations in the electrophoretic system, enantioselectivity of these hydroxyflavanone aglycones could be enhanced with dual CD systems. In this case, SDS monomer acted as a complexing agent probably first with S-beta-CD and then subsequently with the analytes for increasing the effective electrophoretic mobility of the analytes towards the anode and as a selectivity controller for affecting the selectivity of hydroxyflavanones. Better enantioseparation between 2'-hydroxyflavanone and 3'-hydroxyflavanone could be achieved with a dual CD system consisting of S-beta-CD and gamma-CD than that with S-beta-CD and beta-CD. In addition, possible chiral recognition mechanisms of hydroxyflavanones are discussed.     

Chiral separation based on ligand-exchange capillary electrophoresis using a copper(II)-L-ornithine ternary complex as selector

A ligand-exchange capillary electrophoresis was explored, with L-ornithine as the ligand and copper(II) as the central ion. Its applicability was demonstrated with underivatized and dansyl amino acids, a dipeptide, and drugs with amino alcohol structure. The enantioselectivity was found to be strongly dependent on pH and copper(II)-L-Orn complex concentration. Due to the adsorption of the positively charged species onto the capillary inner walls, the chiral separation selectivity is very high while the efficiency is relatively low. Permanent 1,3-propanediamine-coated capillaries show an improved separation efficiency and theoretical plate numbers increasing from 10(4) to 10(5). Similar phenomena were observed when sodium dodecyl sulfate (SDS) micelles were added to the copper(II) complex solution. The poor separation efficiency of chiral compounds in uncoated capillaries may result from the low rate of the ligand-exchange reactions, and the high enantioselectivity may derive from the complexing process in the adsorbed phase.     

Application of carboxymethyl-beta-cyclodextrin as a chiral selector in capillary electrophoresis for enantiomer separation of selected neurotransmitters

The aim of this work was to optimize conditions for capillary electrophoresis separation of different neurotransmitters (serotonin, phenylalanine, dopamine, adrenaline, ephedrine, propranolol and DOPA) in a single run, including separation of existing enantiomers. As chiral selectors added to the borate background, electrolyte unsubstituted alpha-, beta- and -gamma-cyclodextrins (CDs), methyl-, dimethyl-, and trimethyl-substituted beta-CDs, and hydroxypropyl-substituted alpha-, beta- and gamma-CDs were examined. Also carboxymethyl-beta-CD and succinyl-beta-CD were used for this purpose. In addition to the kind and concentration of chiral selector, some other experimental factors also have been optimized, such as concentration of borate buffer, content of methanol, pH of electrolyte, method of sample introduction into the capillary and washing procedure between consecutive runs. The best results were obtained using 20 mM carboxymethyl-beta-CD in borate buffer of pH 7.5 as running electrolyte and hydrostatic injection. The obtained sensitivity of response (peak height) varied from 0.4 for adrenalines to 2.3 mAU mM(-1) for propranolols. The concentration detection limits (S/N=3) were in the range from 0.04 mM for propranolols to 0.2 mM for adrenalines. The resolution obtained in optimized conditions in a single run was from 0.75 for adrenalins and 1.0 for propranolols up to 2.0 for ephedrines. The developed method was employed for determination of these analytes in brain tissue extracts.     

Evaluation of sulfated maltodextrin as a novel anionic chiral selector for the enantioseparation of basic chiral drugs by capillary electrophoresis

Introducing a new class of chiral selectors is an interesting work and this issue is still one of the hot topics in separation science and chirality. In this study, for the first time, sulfated maltodextrin (MD) was synthesized as a new anionic chiral selector and then it was successfully applied for the enantioseparation of five basic drugs (amlodipine, hydroxyzine, fluoxetine, tolterodine, and tramadol) as model chiral compounds using CE. This chiral selector has two recognition sites: a helical structure and a sulfated group which contribute to three corresponding driving forces; inclusion complexation, electrostatic interaction, and hydrogen binding. Under the optimized condition (buffer solution: 50 mM phosphate (pH 3.0) and 2% w/v sulfated MD; applied voltage: 18 kV; temperature: 20°C), baseline enantioseparation was observed for all mentioned chiral drugs. When instead of sulfated MD neutral MD was used under the same condition, no enantioseparation was observed which means the resolution power of sulfated MD is higher than neutral MD due to the electrostatic interaction between sulfated groups and protonated chiral drugs. Also, the countercurrent mobility of negatively charged MD (sulfated MD) allows more interactions between the chiral selector and chiral drugs and this in turn results in a successful resolution for the enantiomers. Furthermore, a higher concentration of neutral MD (approximately five times) is necessary to achieve the equivalent resolution compared with the negatively charged MD.     

Heptakis(6-amino-6-deoxy)-beta-cyclodextrin as a chiral selector for the separation of anionic analyte enantiomers by capillary electrophoresis

A hepta-substituted beta-cyclodextrin bearing seven amino groups, heptakis(6-amino-6-deoxy)-beta-cyclodextrin (per-6-NH2-beta-CD) was successfully used as a chiral selector for the enantioseparation of different anionic analytes. The running buffer pH and chiral selector concentration were the studied parameters crucial in achieving the maximum possible enantioresolution. Enantiomeric separation of a mixture of seven carboxybenzyl-amino acids was achieved in 24 min. Excellent resolution was obtained for carboxybenzyl-tryptophan (Rs = 11.2).     

Hydroxyethylammonium monosubstituted cyclodextrin as chiral selector for capillary electrophoresis

A novel cationic cyclodextrin, mono-6^A-(2-hydroxyethyl-1-ammonium)-6^A-β-cyclodextrin chloride (HEtAMCD) has been successfully synthesized and applied as chiral selector in capillary electrophoresis. The NMR study revealed this chiral selector has three recognition sites: β-CD, ammonium cation and hydroxy group in the sidearm to contribute three corresponding driving forces including inclusion complexation, electrostatic interaction and hydrogen bonding. The effect of buffer pH and HEtAMCD concentration (2.5–10 mM) on enantioselectivity, chiral resolution as well as effective mobility of analytes was investigated. This elegantly designed CD exhibits outstanding enantioselectivities toward the studied hydroxyl acids and ampholytic racemates in CE with the aid of extra hydrogen bonding. Under optimum pH 6.0, chiral resolutions over 5 can be readily obtained for hydroxy acids with CD concentration below 5 mM. The comparison study between HEtAMCD and our earlier reported ammonium CDs indicates the hydroxyethylammonium group of HEtAMCD significantly increased the enantioselective capability.     

Comparative studies of various run buffers for chiral capillary electrophoresis using chiral crown ether as a chiral selector

In the capillary electrophoretic separation of primary amine enantiomers using (+)-(18-crown-6)-tetracarboxylic acid (18C6H4) as a chiral selector, the presence of run buffer constituents such as tris(hydroxymethyl)aminomethane (Tris) or Na+ competing with analytes for 18C6H4, diminishes the effectiveness of 18C6H4. In order to determine appropriate buffer systems for 18C6H4, various run buffer cationic components including Tris, 1,3-bis[tris(hydroxymethyl)methylamino]propane, bis(2-hydroxyethyl)iminotris(hydroxymethyl)methane, triethanolamine, tetramethylammonium, and Na+ were compared. Quantitative studies of the effects of the competitive constituents were carried out by measuring the electrophoretic mobilities of histidine as a function of the 18C6H4 concentration. We also derived a simple equation to estimate the optimal chiral selector concentration for a maximum mobility difference in the presence of a competitive inhibitor.