Separation of diastereomers of a 1,3-disubstituted tetrahydro-β-carboline by capillary electrophoresis with β-cyclodextrin

Summary Capillary zone electrophoresis with -cyclodextrin as electrolyte additive has been investigated for the separation of the diastereomers of a 1,3-disubstituted tetrahydro--carboline. The effects of pH, buffer concentration, -cyclodextrin concentration and applied voltage on resolution were investigated. This study shows that optimizing the assay conditions leads to maximum chiral separation or resolution. The method enables further research on the quantitative analysis of these compounds.     

Chiral separation of pheniramine by capillary electrophoresis partial-filling technique using hydroxypropyl-β-cyclodextrin as chiral selector

A simple capillary electrophoresis partial-filling technique for the enantioseparation of pheniramine is presented. Phosphate buffer and hydroxypropyl-β-cyclodextrin (HP-β-CD) were used as the electrolyte and chiral selector, respectively. Several experimental parameters such as HP-β-CD concentration, HP-β-CD plug length, CE temperature and applied voltage were studied. Under the selected conditions, pheniramine enantiomers can be separated within less than 14 min. The assay was validated for linearity (5.0 × 10⁻⁶–5.0 × 10⁻⁴ M; R ² = 0.9987), limit of detection (5.0 × 10⁻⁷ M), limit of quantitation (5.0 × 10⁻⁶ M), analytical precision (%RSD ≤ 9.8) and accuracy (%recovery = 101 ± 3). The proposed methodology was then applied to the analysis of a commercially available pharmaceutical eye drop preparation. The results are in good agreement with that declared by the manufacturer. The proposed methodology provides adequate results in terms of simplicity, cost, sample throughput, repeatability and accuracy for quality control of pheniramine enantiomers in pharmaceutical preparations.     

Enantiomeric separation and determination of the enantiomeric impurity of armodafinil by capillary electrophoresis with sulfobutyl ether-β-cyclodextrin as chiral selector

A selective capillary electrophoresis method using sulfobutyl ether-β-cyclodextrin as a chiral selector was developed and validated for the determination of the enantiomeric impurity of (R)-modafinil, i.e., armodafinil. Several parameters were optimized for a satisfactory enantioresolution, including the type and concentration of chiral selector and organic modifier, pH of background electrolyte (BGE), capillary temperature. The finally adopted condition was: 20 mmol/L phosphate buffer at pH 7.5, containing 20 mmol/L sulfobutyl ether-β-cyclodextrin and 20% methanol, at temperature of 25 °C. A good resolution of 3.3 for the two enantiomers of modafinil was achieved by applying the optimal conditions. The limit of detection (LOD) and limit of quantification (LOQ) of (S)-modafinil were 1.25 μg/mL and 2.50 μg/mL, respectively. The established method was also proven to display good selectivity, repeatability, linearity and accuracy. Finally, the method was used to investigate the enantiomeric purity of armodafinil in bulk samples.     

Trace analysis of acetylcholinesterase inhibitors with antipsychotic drugs for Alzheimer’s disease by capillary electrophoresis with on column field-amplified sample injection

A simple and sensitive capillary zone electrophoresis (CZE) with UV detection (214 nm) was developed and validated for the simultaneous determination of the acetylcholinesterase inhibitors (AChEI), donepezil, and rivastigmine, with antipsychotic drugs in plasma. A sample pretreatment by liquid–liquid extraction and subsequent quantification by CZE with field-amplified sample injection (FASI) was used. The optimum separation for these analytes was achieved in <20 min at 25 °C with a fused-silica capillary column of 60.2 cm?×?50 μm I.D. (effective length 50 cm) and a run buffer containing 120 mM phosphate (pH 4.0) with 0.1 % γ-cyclodextrin, 40 % methanol (MeOH), and 0.02 % polyvinyl alcohol as a dynamic coating to reduce analytes’ interaction with the capillary wall. Using phenformin as an internal standard (40.0 ng/mL), the linear ranges of the proposed method for the simultaneous determination of donepezil, rivastigmine, aripiprazole, quetiapine, risperidone, clozapine, ziprasidone, and trazodone were over the range 4.0–80.0 ng/mL, and olanzapine was over the range 1.0–20.0 ng/mL. The method was applied for concentrations monitoring of AChEIs and antipsychotic drugs in ten Alzheimer’s disease patients with behavioral and psychological symptoms of dementia after oral administration of the commercial products.

Separation of chiral basic drugs with sulfobutyl-β-cyclodextrin in capillary electrophoresis

Summary Separation of the enantiomers of 22 chiral basic drugs not previously separated with sulfobutyl-β-cyclodextrin (SBE-β-CD) as a chiral selector has been investigated by capillary zone electrophoresis. By dissolving the drug in Britton-Robinson buffer then optimization of selector concentration, pH, and amount injected, the enantiomers of 19 drugs were successfully separated, two for the first time.     

Large‐volume sample stacking with polarity switching for analysis of azo dyes in water samples by capillary electrophoresis

ABSTRACT

A simple, fast and efficient on-line pre-concentration method (large-volume sample stacking) by capillary electrophoresis was proposed for determination of azo dyes residues (allura red [AR], sunset yellow [SY] and tartrazine [TAR]) in water samples. Pre-concentration variables involved in the system were optimised using of a Box–Bhenken design. Under the optimal conditions: injection time 150.0 s, pre-concentration time 120.0 s and reverse potential ?8.0 kV, the proposed methodology improved the analytical sensibility achieving limits of detection of 21.0–41.4 µg L^?1 with enrichment factors of 82.1–210.8 fold. The large-volume sample stacking-capillary electrophoresis method was validated and applied to determine azo dyes residues in 20 water samples (bottled, spring and tap water). Two samples were positive for sunset yellow and tartrazine with a concentration of 25.3 and 30.2 µg L^?1 and % RSD less than 10.0% in all cases.     

Determination of pheniramine enantiomers in eye drop by capillary electrophoresis using hydroxypropyl-β-cyclodextrin as chiral selector

A capillary zone electrophoresis procedure has been developed for the chiral determination of pheniramine in eye drop. Native and derivative cyclodextrins (CDs) including γ-CD, β-CD, hydroxypropyl-β-CD and dimethyl-β-CD were tested as chiral selectors. Using 30 mM hydroxypropyl-β-CD in 50 mM phosphate buffer (pH 3.0), the acceptable resolution value (R = 1.55) was obtained. The assay was validated for linearity (3.3 × 10⁻⁶–5.0 × 10⁻⁴ M; R ² = 0.9996), limit of detection (3.3 × 10⁻⁶ M), limit of quantification (8.5 × 10⁻⁶ M), analytical precision by terms of intra- and inter-day variability (RSD ≤ 2.57%), and accuracy (recovery ≥ 89.3%). The content of pheniramine in eye drop obtained by the proposed method was in good agreement with the declared value. The results indicated that pheniramine in the eye drop was present as the racemate.     

Analysis of carbamazepine and its five metabolites in serum by large-volume sample stacking–sweeping capillary electrophoresis

This study establishes a method, using different buffer conductivities and large-volume sample stacking (LVSS)–sweeping capillary electrophoresis, for analysis of carbamazepine (CBZ) and its five metabolites in serum. The capillary (50/60 cm) was filled with a high concentration of background electrolyte (150 mM phosphate, pH?3.5, containing 15 % methanol), followed by a large volume of samples (10 psi, 20 s) with low-concentration buffers (5 mM phosphate, pH?3.5, with 5 % methanol). When high voltage was applied (?20 kV), the sodium dodecyl sulfate (SDS) started to sweep the analytes to an outlet. Meanwhile, the analytes decelerated at the boundary between low- and high-conductivity buffers. Finally, a narrow sample zone was formed. The procedure of sweeping and separation was simultaneously carried out by a sweeping buffer (150 mM phosphate, pH?3.5) with 15 % methanol and 50 mM SDS added, and the detection was performed by UV at 214 nm. The method was validated for linearity (r?≧?0.997), precision, and accuracy. The calibration curves were established for CBZ and its five metabolites between 0.03–25 and 0.03–3 μg/mL. The limits of detection (S/N?=?3) were 0.01 μg/mL for each analyte. Compared with simple MEKC (0.5 psi, 5 s), this system can improve the sensitivity about 300-fold. Finally, this method was successfully applied to five patients, who had taken 200 mg CBZ daily, and CBZ levels were found to be from 3.72 to 5.82 μg/mL.

Sequential preconcentration by coupling of field amplified sample injection with pseudo isotachophoresis–acid stacking for analysis of alkaloids in capillary electrophoresis

A novel on-column sequential preconcentration method based on the combination of field-amplified sample injection induced by acetonitrile and pseudo isotachophoresis (ITP)–acid stacking is developed for simply but efficiently concentrating alkaloid cations in a high-salt sample matrix in capillary electrophoresis. Acetonitrile (70%) added to a sample solution with a high-salt sample matrix not only induces field-amplified sample stacking by decreasing conductivity but also acts as a termination reagent in the succeeding pseudo ITP. After sample injection had been completed, a plug of H⁺ was injected electrokinetically and a neutralization reaction between H⁺ and tartrate from the buffer solution produced a low conductivity zone, in which the injected analyte cations were further concentrated. With the sequential preconcentration method, a 3 orders of magnitude detection sensitivity (1,400-fold) increase could be observed compared with the conventional electrokinetic injection method, without compromising separation efficiency and peak shape, and detection limits of 0.1 ng/mL for myosmine and 0.3 ng/mL for anabasine with the conditions selected were achieved. The calibration curves demonstrated good linearity in the concentration ranges 1.3–600 ng/mL for myosmine and 4.9–900 ng/mL for anabasine, respectively. The proposed method has been used to analyze successfully trace alkaloids in cigarette samples. Figure Sequential preconcentration processes: a sample injection; b introduction of HCl; c capillary zone electrophoresis separation. A ⁻ tartrate, white circles acetonitrile, black circles Na⁺, sample zone, myosmine, anabasine     

Analysis of repaglinide enantiomers in pharmaceutical formulations by capillary electrophoresis using 2,6-di-o-methyl-β-cyclodextrin as a chiral selector

This study used the general applicability of 2,6-didi-o-methyl-β-cyclodextrin (DM-β-CD) as the chiral selector in capillary electrophoresis for fast and efficient chiral separation of repaglinide enantiomers. A systematic study of the parameters affecting separation was performed with UV detection at 243 nm. The optimum conditions were determined to be 1.25% (w/v) DM-β-CD in 20 mM sodium phosphate (pH 2.5) as the running buffer and separation voltage at 20 kV. DM-β-CD had the best enantiomer resolution properties under the tested conditions, whereas other β-cyclodextrins showed inferior performances or no performance. The proposed method had a linear calibration curve in the concentration range of 12.5-400 μg/mL. The limit of detection was 100 ng/mL. The intra-day and inter-day precisions were 2.8 and 3.2%, respectively. Recoveries of 97.9-100.9% were obtained. The proposed method was fast and convenient, and was determined to be efficient for separating enantiomers and applicable for analyzing repaglinide enantiomers in quality control of pharmaceutical production.     

Direct enantioseparation of lipoic acid in dietary supplements by capillary electrophoresis using trimethyl-β-cyclodextrin as a chiral selector

Lipoic acid, an antioxidant, naturally occurs as the (R)-enantiomer, while synthetic lipoic acid is racemic. It is thus of interest to know the (R)-enantiomer content of lipoic acid supplements. Here, we used capillary electrophoresis to directly enantioseparate lipoic acid in dietary supplements by using a sulfonated capillary with an effective voltage of +18 kV and direct detection at 200 nm. Factors affecting migration time and resolution of lipoic acid were investigated. The optimum background electrolyte was found to be 100 mM phosphate buffer (pH 7.0) containing 8 mM trimethyl-β-cyclodextrin as a chiral selector at 20°C. Under the proposed conditions, direct chiral resolution of lipoic acid in dietary supplements was conducted successfully.     

Enantiomeric separation of dansylamino acids by capillary zone electrophoresis with selectively methylated γ-cyclodextrin derivatives

The chiral separation ability of octakis2-, 3- and 6-mono-O-methyl, 2,3-, 2,6- and 3,6-di-O-methyl, and 2,3,6-tri-O-methyl)-γ-cyclodextrins as chiral selectors in capillary zone electrophoresis was investigated using twelve dansylamino acids. Unmodified and 6-monomethylated -γ-cyclodextrins (γ-CDs) exhibited similar high enantioselectivities. γ-CD still exhibited a chiral separation ability after 2-monomethylation or 2,6-dimethylation. 3-Monomethylated -γ-CD could only separate the enantiomers of two dansylamino acids, but further methylation of the hydroxyl groups at the 6-positions of 3-monomethylated γ-CD resulted in the highest chiral separation ability. γ-CD completely lost its high enantioselectivity after methylation of both the 2- and 3-positions, regardless of 6-methylation.     

Characterization of the complexation of tauro- and glyco-conjugated bile salts with γ-cyclodextrin and 2-hydroxypropyl-γ-cyclodextrin using affinity capillary electrophoresis

The complexation of seven bile salts, present in the small intestine of rat, dog and man, (taurocholate, tauro-β-muricholate, taurodeoxycholate, taurochenodeoxycholate, glycocholate, glycodeoxycholate and glycochenodeoxycholate) with γ-cyclodextrin and the chemically modified 2-hydroxypropyl-γ-cyclodextrin, was studied using affinity capillary electrophoresis (ACE). The cyclodextrins (CDs) were investigated due to their use in drug formulation as excipients for solubilisation of poorly soluble drugs and drug candidates. Using mobility shift ACE, the bile salt cyclodextrin interactions were characterized demonstrating 1:1 binding stoichiometry with stability constants ranging from 2 × 10³ to 8 × 10⁴ M^?1. The binding constants showed a systematic dependence on the number and position of hydroxyl groups on the steroid skeleton and the stability constants were in general higher for complexation with the native cyclodextrin than with the modified cyclodextrin. Based upon the size of the complexation constants, it was suggested that the interaction between the CDs and the bile salts takes place at the C and D ring of the steroid skeleton. The complexation of bile salts with the γ-cyclodextrins may compete with drug-γ-cyclodextrin complex formation and, thus, potentially affect drug absorption and efficacy.     

Separation of chiral drugs with β-CD phosphate by capillary electrophoresis

In capillary electrophoresis (CE) chiral separation is accomplished by adding suitableselector in the running electrolyte"'. The type of selector is of primary importance forachieving successful resolution. Selector concentration has considerable influence aswell3'. Charged cyclodextrins were first introduced for chiral separation of aminoacidss and used for enantioseparation of drugs by Terabe group'. Many kinds ofcharged CDs are now commercially available7-11. The charged CD commonly use…     

Separation of drug enantiomers by capillary electrophoresis: α-cyclodextrin as chiral solvating agent

Summary Enantiomer separation by capillary zone electrophoresis was studied for a set of 59 chiral drugs. With -cyclodextrin as chiral solvating agent, six enantiomeric pairs could be resolved. Baseline separation was achieved for clidinium bromide, oxomemazine and tetryzoline, whereas ketamine, orphenadrine, tropicamide and others require further optimization. Aliphatic and monocyclic compounds prevail among compounds recognized by -cyclodextrin. Statistical analysis reveals that a medium degree of migration retardation offers the best chance for successful separation.Part II. For Part I see reference [18].     

Use of methylamino-β-cyclodextrin in capillary electrophoresis. Resolution of acidic and basic enantiomers

Summary -cyclodextrin derivatives, namely 6^A methylamino--CD and hepta-methylamino--CD have been used as chiral selectors for the enantiomeric separation of a number of acidic and basic compounds by capillary electrophoresis employing either coated or uncoated capillaries. The effects of the CD type and concentration and the pH of the background electrolyte on the mobility and chiral resolution of the analytes have been studied. The use of monomethylamino--CD in a coated capillary allowed the enantiomeric resolution of phenyl lactic acid, warfarin and acenocoumarol but was not successful for tiaprofen and its 3-isomer. The heptamethylamino derivative, under the same experimental conditions, was a better chiral selector than the monosubstuted CD toward the arylpropionic acids and phenyl lactic acid while the anticoagulant drugs showed poor or no chiral resolution. Inversion of migration order was obtained for phenyl lactic acid, warfarin and acenocoumarol enantiomers. The enantiomers of basic compounds of pharmaceutical interest, namely propranolol, terbutaline, ketamine, chlorpheriramine and isoproterenol were only resolved using monomethylamino--CD dissolved in a phosphate buffer containing tetramethylammonium ions.Part of this work was presented at Eighth International Symposium on High Performance Capillary Electrophoresis, HPCE '96, January 21–25, 1996, Orlando, FL, USA.     

Speciation studies by capillary electrophoresis – simultaneous determination of iodide and iodate in seawater

A capillary electrophoresis (CE) method was developed for the simple and highly-sensitive determination of iodine species in seawater. The proposed method is based on the on-capillary preconcentration of iodide and iodate using the principle of transient isotachophoresis (tITP) stacking, and direct UV detection of the separated species at 226 and 210 nm, respectively. The preconcentration procedure takes advantage of the electrokinetic introduction of the terminating ion [2-(N-morpholino)ethanesulfonate (MES)] into the capillary, that enables a longer tITP state. The appropriate conditions for the tITP step were optimized by varying the MES and sample injection time and the concentration of cetyltrimethylammonium chloride (CTAC). The latter component of the separation electrolyte (SE) was shown to strongly affect the migration and therefore the enrichment of iodide due to specific ion-association. The optimized separations were performed in 12.5 mM CTAC, 0.5 M NaCl (pH 2.4). Valid calibration is demonstrated in the range 3–60 g L^–1 iodide (R=0.9992) and 40–800 g L^–1 iodate (R=0.9994). The detection limits achieved were 0.23 g L^–1 (2 nM) for iodide and 10 g L^–1 (57 nM) for iodate. Such sensitivity and linearity thresholds allowed the reported tITP-CE system to be applied to direct speciation analysis of surface and seabed seawater. The comparison of CE results with those of an ion-chromatography (IC) technique proved that the method has acceptable accuracy.     

Solid-phase extraction and field-amplified sample injection–capillary zone electrophoresis for the analysis of benzophenone UV filters in environmental water samples

A field-amplified sample injection–capillary zone electrophoresis (FASI-CZE) method for the analysis of benzophenone (BP) UV filters in environmental water samples was developed, allowing the separation of all compounds in less than 8 min. A 9- to 25-fold sensitivity enhancement was obtained with FASI-CZE, achieving limits of detection down to 21–59 μg/L for most of the analyzed BPs, with acceptable run-to-run and day-to-day precisions (relative standard deviations lower than 17 %). In order to remove water sample salinity and to enhance FASI sensitivity, an off-line solid-phase extraction (SPE) procedure using a Strata X polymeric reversed-phase sorbent was used and afforded recoveries up to 72–90 % for most BPs. With the combination of off-line SPE and FASI-CZE, limits of detection in the range 0.06–0.6 μg/L in a river water matrix, representing a 2,400- to 6,500-fold enhancement, were obtained. Method performance was evaluated by quantifying a blank river water sample spiked at 1 μg/L. For a 95 % confidence level, no statistical differences were observed between found concentrations and spiked concentrations (probability at the confidence level, p value, of 0.60), showing that the proposed off-line SPE-FASI-CZE method is suitable for the analysis of BP UV filters in environmental water samples at low microgram per liter levels. The method was successfully applied to the analysis of BPs in river water samples collected up- and downstream of industrialized and urban areas, and in some drinking water samples.     

Separation of chiral drugs with sulfobutylether-β-cyclodextrin bycapillary zone electrophoresis

IntroductionChaedcyclodextrlnswerefirstIntroducedby几rabelforchlralseparationofamlnoacids,andthechargedCDcommonlyusednowdaysarecarboxymethyl－p－CD（CM－p－CD）,p－CD－phosphate,Y－CD－phosphate,sulfobutylether－p－cyclodextrln（SBE－p－CD）etc．...