Separation of enantiomers of chiral basic drugs with amylose- and cellulose- phenylcarbamate-based chiral columns in acetonitrile and aqueous-acetonitrile in high-performance liquid chromatography with a focus on substituent electron-donor and electron-acceptor effects.

In this study, amylose- and cellulose-phenylcarbamate-based chiral columns with different chiral-selector (CS) chemistries were compared to each other for the separation of enantiomers of basic chiral analytes in acetonitrile and aqueous-acetonitrile mobile phases in HPLC. For two chemistries the amylose-based columns with coated and immobilized CSs were also compared. The comparison of CSs containing only electron-donating or electron-withdrawing substituents with those containing both electron-donating and electron-withdrawing substituents showed opposite results for the studied set of chiral analytes in the case of amylose and cellulose derivatives. Along with the chemistry of CS the focus was on the behavior of polysaccharide phenylcarbamates in acetonitrile versus aqueous acetonitrile as eluents. In agreement with earlier results, it was found that in contrast to the commonly accepted view, polysaccharide phenylcarbamates do not behave as typical reversed-phase materials for basic analytes either. In the range of water content in the mobile phase of up to 20-30% v/v the behavior of these CSs is similar to hydrophilic interaction liquid chromatography (HILIC)-type adsorbents. This means that with increasing water content in the mobile phase up to 20-30% v/v, the retention of analytes mostly decreases. The important finding of this study is that the separation efficiency improves for most analytes when switching from pure acetonitrile to aqueous acetonitrile. Therefore, in spite of reduced retention, the separation of enantiomers improves and thus, the HILIC-range of mobile phase composition, offering shorter analysis time and better peak resolution, is advantageous over pure polar-organic solvent mode. Interesting examples of enantiomer elution order (EEO) reversal were observed for some analytes based on the content of water in the mobile phase on Lux Cellulose-1 and Lux Amylose-2 columns.

Chiral Fluorescent Silicon Nanoparticles for Aminopropanol Enantiomer: Fluorescence Discrimination and Mechanism Identification.

As an important chiral molecule for the preparation of levofloxacin, the optical purity of L-aminopropanol has a crucial effect on the pharmacology and pharmacodynamics of levofloxacin. Therefore, it is of great significance to discriminate D-aminopropanol and L-aminopropanol. In this paper, an effective aminopropanol enantiomer recognition method was established on the basis of the chiral fluorescent silicon nanoparticles (SiNPs) probe. The chiral fluorescent SiNPs were fabricated via a one-step aqueous solution synthesis strategy, which avoided multiple steps, pressurizing operation, and time-consuming postmodified procedures. Significantly, D-aminopropanol could significantly enhance the fluorescence of the chiral SiNPs, while L-aminopropanol could not affect the fluorescence of the chiral SiNPs. This could have occurred because of the stronger interaction between the chiral SiNPs and D-aminopropanol than that of L-aminopropanol. Thus, the rapid and selective recognition of the aminopropanol enantiomer was ideally realized. The mechanism of the chiral SiNPs recognizing aminopropanol was simulated by density functional theory quantum mechanical calculations. Interestingly, this was also proved by the separation of aminopropanol enantiomer using this chiral SiNPs-modified silica column in normal phase liquid chromatography. To the best of our knowledge, this is the first time that the chiral fluorescent SiNPs were synthesized and used to detect the aminopropanol enantiomer successfully. This work will inspire additional syntheses of chiral silicon nanomaterials and other nanomaterials with excellent properties and will enable application of chiral nanomaterials to other fields.

Metal organic framework HKUST-1 modified with carboxymethyl-ß-cyclodextrin for use in improved open tubular capillary electrochromatographic enantioseparation of five basic drugs.

This work shows that the metal organic framework (MOF) HKUST-1 of type Cu3(BTC)2 (also referred to as MOF-199; a face-centered-cubic MOF containing nanochannels) is a most viable coating for use in enantioseparation in capillary electrochromatography (CEC). A HKUST-1 modified capillary was prepared and characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, elemental analysis and thermogravimetric analysis. CEC-based enantioseparation of the basic drugs propranolol (PRO), esmolol (ESM), metoprolol (MET), amlodipine (AML) and sotalol (SOT) was performed by using carboxymethyl-ß-cyclodextrin as the chiral selector. Compared with a fused-silica capillary, the resolutions are improved (ESM: 1.79; MET: 1.80; PRO: 4.35; SOT: 1.91; AML: 2.65). The concentration of chiral selector, buffer pH value, applied voltage and buffer concentration were optimized, and the reproducibilities of the migration times and Rs values were evaluated. Graphical abstract Schematic presentation of the preparation of a HKUST-1@capillary for enantioseparation of racemic drugs. Cu(NO3)2 and 1,3,5-benzenetricarboxylic acid (BTC) were utilized to prepare the HKUST-1@capillary. Then the capillary was applied to construct capillary electrochromatography system with carboxymethyl-ß-cyclodextrin (CM-ß-CD) for separation of basic racemic drugs.

Development of liquid chromatographic methods for enantioseparation and sensitive detection of ß-adrenolytics/ß2-agonists in human plasma using a single enantiomer reagent.

Enantioseparation of four commonly used ß-adrenolytics (bisoprolol, salbutamol, and carvedilol, marketed as racemic mixtures) has been achieved by both TLC and RPHPLC via an indirect approach. A new chiral reagent, (S)-naproxen benzotriazole ester, was synthesized and it was characterized by UV, IR, 1HNMR, elemental analysis and polarimetry. It was used to synthesize diastereomeric derivatives of the three ß-adrenolytics under microwave irradiation. TLC separation of diastereomeric derivatives was achieved which were then isolated by preparative approach; these were characterized and were used as standard reference for determining absolute configuration of diastereomeric derivatives and for establishing validated HPLC method for enantioseparation and sensitive detection of the three ß-adrenolytics in human plasma. Mobile phase in gradient mode containing methanol and aqueous triethylaminephosphate (TEAP) was successful for HPLC separation; conditions with respect to pH, flow rate, and buffer concentration were optimized. The method is capable to accurately quantitate ß-adrenolytics in human plasma with minimal sample clean-up and rapid separation by TLC and RPHPLC. The limit of detection values were 0.97 and 0.87ng/mL for diastereomeric derivatives of (S)- and (R)-bisoprolol, respectively, which are very low in comparison to literature reports.

Carboxymethyl ß-cyclodextrin as chiral selector in capillary electrophoresis: Enantioseparation of 16 basic chiral drugs and its chiral recognition mechanism associated with drugs' structural features.

Herein we present the enantioseparation of 10 cardiovascular agents and six bronchiectasis drugs including propranolol, carteolol, metoprolol, atenolol, pindolol, esmolol, bisoprolol, bevantolol, arotinolol, sotalol, clenbuterol, procaterol, bambuterol, tranterol, salbutamol and terbutaline sulfate using carboxymethyl-ß-cyclodextrin (CM-ß-CD) as chiral selector. To our knowledge, there is no literature about using CM-ß-CD for separating carteolol, esmolol, bisoprolol, bevantolol, arotinolol, procaterol, bambuterol and tranterol. During the course of work, changes in pH, CM-ß-CD concentration, buffer type and concentration were studied in relation to chiral resolution. Excellent enantiomeric separations were obtained for all 16 compounds, especially for procaterol. An impressive resolution value, up to 17.10, was obtained. In particular, most of them achieved rapid separations within 20 min. Given the fact that enantioseparation results rely on analytes' structural characters, the possible separation mechanisms were discussed. In addition, in order to obtain faster separation for propranolol enantiomers in practical application, the effective length of capillary was innovatively shortened from 45 to 30 cm. After the validation, the method was successfully applied to the enantiomeric purity determination of propranolol in the formulation of drug substances.

Determination of propranolol and carvedilol in urine samples using a magnetic polyamide composite and LC-MS/MS.

AIM: ß-blockers are compounds that bind with adrenoreceptors hindering their interaction with adrenalin and noradrenalin. They are clinically relevant and they are also used in some sport as doping agents. RESULTS: A new method based on the combination of dispersive micro-solid phase extraction and LC-MS/MS has been developed to determine propranolol and carvedilol in urine samples. For this purpose a magnetic-polyamide composite is synthesized and used as sorbent. Working under the optimum conditions, the method provides limits of detection and quantification in the range of 0.1-0.15 µg/l and 0.3-0.5 µg/l, for carvedilol and propranolol, respectively. The precision, expressed as RSD, was better than 9.6% and the relative recoveries varied between 73.7 and 81.3%. CONCLUSION: The methodology is appropriate for the determination of ß-blockers in urine samples at the low microgram per liter range for therapeutic purposes.

Capillary electrophoretic enantioseparation of basic drugs using a new single-isomer cyclodextrin derivative and theoretical study of the chiral recognition mechanism.

A novel single-isomer cyclodextrin derivative, heptakis {2,6-di-O-[3-(1,3-dicarboxyl propylamino)-2-hydroxypropyl]}-ß-cyclodextrin (glutamic acid-ß-cyclodextrin) was synthesized and used as a chiral selector in capillary electrophoresis for the enantioseparation of 12 basic drugs, including terbutaline, clorprenaline, tulobuterol, clenbuterol, procaterol, carvedilol, econazole, miconazole, homatropine methyl bromide, brompheniramine, chlorpheniramine and pheniramine. The primary factors affecting separation efficiency, which include the background electrolyte pH, the concentration of glutamic acid-ß-cyclodextrin and phosphate buffer concentration, were investigated. Satisfactory enantioseparations were obtained using an uncoated fused-silica capillary of 50 cm (effective length 40 cm) × 50 µm id with 120 mM phosphate buffer (pH 2.5-4.0) containing 0.5-4.5 mM glutamic acid-ß-cyclodextrin as background electrolyte. A voltage of 20 kV was applied and the capillary temperature was kept at 20°C. The results proved that glutamic acid-ß-cyclodextrin was an effective chiral selector for studied 12 basic drugs. Moreover, the possible chiral recognition mechanism of brompheniramine, chlorpheniramine and pheniramine on glutamic acid-ß-cyclodextrin was investigated using the semi-empirical Parametric Method 3.

Preparation of a ß-Cyclodextrin-Based Open-Tubular Capillary Electrochromatography Column and Application for Enantioseparations of Ten Basic Drugs.

An open-tubular capillary electrochromatography column was prepared by chemically immobilized ß-cyclodextrin modified gold nanoparticles onto new surface with the prederivatization of (3-mercaptopropyl)-trimethoxysilane. The synthesized nanoparticles and the prepared column were characterized by transmission electron microscopy, scanning electron microscopy, infrared spectroscopy and ultraviolet visible spectroscopy. When the column was employed as the chiral stationary phase, no enantioselectivity was observed for ten model basic drugs. So ß-cyclodextrin was added to the background electrolyte as chiral additive to expect a possible synergistic effect occurring and resulting in a better separation. Fortunately, significant improvement in enantioselectivity was obtained for ten pairs of drug enantiomers. Then, the effects of ß-cyclodextrin concentration and background electrolyte pH on the chiral separation were investigated. With the developed separation mode, all the enantiomers (except for venlafaxine) were baseline separated in resolutions of 4.49, 1.68, 1.88, 1.57, 2.52, 2.33, 3.24, 1.63 and 3.90 for zopiclone, chlorphenamine maleate, brompheniramine maleate, dioxopromethazine hydrochloride, carvedilol, homatropine hydrobromide, homatropine methylbromide, venlafaxine, sibutramine hydrochloride and terbutaline sulfate, respectively. Further, the possible separation mechanism involved was discussed.

A dispersive liquid-liquid microextraction and chiral separation of carvedilol in human plasma using capillary electrophoresis.

BACKGROUND: Development of simple, rapid and precise analysis of chiral drugs in biological samples is an important issue. Dispersive liquid-liquid microextraction in combination with CE using field amplified sample injection has been of interest because of its capability to analyze trace amount of drugs. METHODS: Dispersive liquid-liquid microextraction-CE-field amplified sample injection was employed for chiral separation of carvedilol in human plasma using UV-DAD detector and the developed method has been validated according to US FDA method validation guideline for bioanalysis. RESULTS: The method was linear over a concentration range of 12.5-100 ng/ml for each carvedilol enantiomer (R(2) = 0.998) and the mean recoveries ranged from 91 to 107%. CONCLUSION: The method was adapted for sensitive, selective and rapid determination of carvedilol enantiomers in human plasma samples.

Ionic liquid phase microextraction combined with fluorescence spectrometry for preconcentration and quantitation of carvedilol in pharmaceutical preparations and biological media.

BACKGROUND: Carvedilol belongs to a group of medicines termed non-selective beta-adrenergic blocking agents. In the presented approach, a practical and environmentally friendly microextraction method based on the application of ionic liquids (ILs) was followed by fluorescence spectrometry for trace determination of carvedilol in pharmaceutical and biological media. METHODS: A rapid and simple ionic liquid phase microextraction was utilized for preconcentration and extraction of carvedilol. A hydrophobic ionic liquid (IL) was applied as a microextraction solvent. In order to disperse the IL through the aqueous media and extract the analyte of interest, IL was injected into the sample solution and a proper temperature was applied and then for aggregating the IL-phase, the sample was cooled in an ice water-bath. The aqueous media was centrifuged and IL-phase collected at the bottom of the test tube was introduced to the micro-cell of spectrofluorimeter, in order to determine the concentration of the enriched analyte. RESULTS: Main parameters affecting the accuracy and precision of the proposed approach were investigated and optimized values were obtained. A linear response range of 10-250 µg I(-1) and a limit of detection (LOD) of 1.7 µg I(-1) were obtained. CONCLUSION: Finally, the presented method was utilized for trace determination of carvedilol in commercial pharmaceutical preparations and biological media.

Spherical ß-cyclodextrin-silica hybrid materials for multifunctional chiral stationary phases.

Spherical ß-CD-silica hybrid materials have been prepared successfully by simple one-pot polymerization, which provide a new strategy to construct new type of HPLC chiral stationary phases. Various ß-CD, ethane, triazinyl and 3,5-dimethylphenyl functional groups that can provide multiple interactions were introduced into the pore channels and pore wall framework of mesoporous materials, respectively. The materials towards some chiral, acidic, anilines and phenols compounds showed multiple chromatographic separation functions including racemic resolution, anion exchange and achiral separations with a typical feature of normal/reversed phase chromatography. Multi-tasking including racemic resolution and achiral separations for selected compounds were performed simultaneously on a chiral chromatographic column. The multifunctional character of materials arises from the multiple interactions including hydrophobic interaction, π-π interaction, anion exchange, inclusion interaction and hydrogen bonding interaction.

Validated stability-indicating capillary electrophoresis method for the separation and determination of a fixed-dose combination of carvedilol and hydrochlorothiazide in tablets.

A novel, fast, sensitive, and specific capillary electrophoresis (CE) technique coupled to a diode array detector has been developed for the separation and simultaneous determination of carvedilol (CRV) and hydrochlorothiazide (HCT) in two combination formulations. The proposed method utilized a fused silica capillary (55 cm x75 microm id) and the background electrolyte solution phosphate buffer (12.5 mM, pH 7.4)-methanol (95+5, v/v). The separation was achieved at 30 kV applied voltage and 24 degree C. Atorvastatin (80 microg/mL) was chosen as the internal standard. The described method was linear over the range of 1-200 and 0.2-150 microg/mL for CRV and HCT, respectively. Intraday and interday RSD (n = 6) was < or =1.4%. The LOD values of CRV and HCT were 0.26 and 0.07 microg/mL, respectively. The validated CE method was successfully applied to the analysis of two commercial tablet dosage forms. Forced degradation studies were performed on bulk samples of the two drugs using thermal, photolytic, hydrolytic, and oxidative stress conditions, and the stressed samples were analyzed by the proposed method. Degradation products produced as a result of stress studies did not interfere with the determination of CRV and HCT; the assay could, therefore, be considered stability-indicating.

New single isomer negatively charged ß-cyclodextrin derivatives as chiral selectors in capillary electrophoresis.

To improve resolution power of chiral selector and enantiomeric peak efficiency in CE, single isomer negatively charged ß-CD derivatives, mono(6-deoxy-6-sulfoethylthio)-ß-CD (SET-ß-CD) bearing one negative charge and mono[6-deoxy-6-(6-sulfooxy-5,5-bis-sulfooxymethyl)hexylthio]-ß-CD (SMHT-ß-CD) carrying three negative charges, were synthesized. The structure of these two ß-CD derivatives was confirmed by (1)H NMR and MS. SET-ß-CD and SMHT-ß-CD successfully resolved the enantiomers of several basic model compounds. SMHT-ß-CD provided for a significantly greater enantioseparation than SET-ß-CD at lower concentrations. This appears to be due to the higher binding affinity of SMHT-ß-CD to the model compounds and the wider separation window resulting from an increased countercurrent mobility of the selector. Overall, the new chiral selectors provided enantioseparations with high peak efficiency while avoiding peak distortion due to polydispersive and electrodispersive effects. The information obtained from an apparent binding constant study suggested that the enantioseparation of the model compounds followed the predictions of charged resolving agent migration model and that the observed degree of enantioseparation difference were due to the magnitude of differences in both enantiomer-chiral selector binding affinities (ΔK) and the mobilities of the complexed enantiomers (Δµ(c)).

Chiral separation of ß-blockers by MEEKC using neutral microemulsion: Analysis of separation mechanism and further elucidation of resolution equation.

Based on the investigation of the effect of microemulsion charge on the chiral separation, a new chiral separation method with MEEKC employing neutral microemulsion was established. The method used a microemulsion containing 3.0% (w/v) neutral surfactant Tween 20 and 0.8% (w/v, 30 mM) dibutyl l-tartrate in 40 mM sodium tetraborate buffer to separate the enantiomers of ß-blockers. The effect of major parameters on the chiral separation was investigated. The applied voltage had little effect on the resolution, but the chiral separation could be improved by suppressing the EOF. Nine racemic ß-blockers obtained relatively good enantioseparation after appropriate concentrations of tetradecyl trimethyl ammonium bromide were added into the microemulsion to suppress the EOF. These results were explained based on the analysis of the separation mechanism of the method and deduced separation equations. The resolution equation of the method was further elucidated. It was found that the fourth term in the resolution equation, an additional term compared to the conventional resolution equation for column chromatography, represents the ratio of the relative movement distance between the analyte and microemulsion droplets relative to the effective capillary length. It can be regarded as a correction for the effective capillary length. These findings are significant for the development of the theory of MEEKC and the development of new chiral MEEKC method.

Enantioselective LC/ESI-MS/MS analysis and pharmacokinetic and tissue distribution study of (2RS)-1-(7-methoxy-1H-indol-4-yloxy)-3-(2-(2-methoxyphenoxy)ethylamino)-propan-2-ol in rats.

A sensitive and stereospecific liquid chromatography-tandem mass spectrometry method for the quantitative determination of TWo8 enantiomers ((2RS)-1-(7-methoxy-1H-indol-4-yloxy)-3-(2-(2-methoxyphenoxy)ethylamino)-propan-2-ol) was developed and validated in rat serum and some tissues. Racemic TWo8 is a new chemical entity, and it has been shown to possess pharmacological activity in vivo. The assay involved the diastereomeric derivatization of racemic TWo8 with 2,3,4,6-tetra-O-acetyl-beta-glucopyranosyl isothiocyanate. The TWo8 diastereoisomers quantification was performed on a triple quadrupole mass spectrometer employing an electrospray ionization technique. The precursor to the product ion transition for TWo8 derivatives and for the internal standard (carbamazepine) was m/z 776.4 → 387.2 and 237.4 → 194.4, respectively. The assay was validated with a linear range of 10-2000 ng/ml of racemic TWo8. The inter-day precisions for (-)-(S)-TWo8 and (+)-(R)-TWo8 were 2.1% to 14.9% and 1.3% to 14.8%, respectively. The inter-day accuracy for (-)-(S)-TWo8 and (+)-(R)-TWo8 was within 86% to 114% and 91% to 114%, respectively. A pilot pharmacokinetic study of this new ß-adrenolytic compound has shown that (-)-(S)-TWo8 is eliminated faster than its antipode. The terminal half-lives of (-)-(S)-TWo8 and (+)-(R)-TWo8 were 3.2 and 3.9 h, respectively. The compound distribution into different organs, evaluated in tissue homogenate samples following TWo8 intravenous administration, showed an enantioselective penetration of TWo8 enantiomers in the liver (p < 0.03), in the kidney (p < 0.001), and in the lungs (p < 0.05). The developed method using liquid chromatography-tandem mass spectrometry method with electrospray ionization could be employed for quantitative determination of compounds with similar structure.

[Chiral separation of five beta-blockers using di-n-hexyl L-tartrate-boric acid complex as mobile phase additive by reversed-phase liquid chromatography].

A reversed-phase high performance liquid chromatographic (HPLC) method using the di-n-hexyl L-tartrate-boric acid complex as a chiral mobile phase additive was developed for the enantioseparation of five beta-blockers including propranolol, esmolol, metoprolol, bisoprolol and sotalol. In order to obtain a better enantioseparation, the influences of concentrations of di-n-butyl L-tartrate and boric acid, the type, concentration and pH of the buffer, methanol content as well as the molecular structure of analytes were extensively investigated. The separation of the analytes was performed on a Venusil MP-C18 column (250 mm x 4.6 mm, 5 microm). The mobile phase was 15 mmol/L ammonium acetate-methanol containing 60 mmol/L boric acid, 70 mmol/L di-n-hexyl L-tartrate (pH 6.00). The volume ratios of 15 mmol/L ammonium acetate to methanol were 20: 80 for propranolol, esmolol, metoprolol, bisoprolol and 30: 70 for sotalol. The flow rate was 0.5 mL/min and the detection wavelength was set at 214 nm. Under the optimized conditions, baseline enantioseparation was obtained separately for the five pairs of analytes.

Stir bar sorptive extraction and high performance liquid chromatographic determination of carvedilol in human serum using two different polymeric phases and an ionic liquid as desorption solvent.

This article presents a method employing stir bar coated with a film of poly (methyl methacrylate/ethyleneglycol dimethacrylate) (PA-EG) and polydimethylsiloxane (PDMS) in combination with liquid desorption (LD) using ionic liquid, followed by high performance liquid chromatography (HPLC) equipped with ultraviolet (UV) detection for the determination of carvedilol in human serum samples. Stir bar sorptive extraction (SBSE) variables, such as desorption and extraction time and temperature, desorption solvent and pH of the matrix were optimized, in order to achieve suitable analytical sensitivity in a short period of time. Also, the concentration effect of 1-methyl-3-octylimidazolium tetrafluoroborate [Omim][BF4] ionic liquid on the efficiency of LD was investigated. A comparison between PA-EG/SBSE and PDMS/SBSE was made by calculating the experimental recovery and partition coefficient (K), where PA-EG phase demonstrated to be an excellent alternative for the enrichment of the carvedilol from serum samples. The effect of [Omim][BF4] on carryover was studied and no carryover was observed. Under optimized experimental conditions, the analytical performance showed excellent linear dynamic range, with correlation coefficients higher than 0.999 and limits of detection and quantification of 0.3 and 1.0 ng mL(-1), respectively. Intra- and inter-day recovery ranged from 94 to 103% and the coefficients of variations were less than 3.2%. The proposed method was shown to be simple, highly sensitive and suitable for the measurement of trace concentration levels of carvedilol in biological fluid media.

Comparison of reversed-phase and hydrophilic interaction liquid chromatography for the separation of ephedrines.

The separation of highly basic solutes is an ongoing challenge, especially in achieving suitable retention and peak shapes for compounds such as ephedrines that have both high pK(a) values (≥ 9.3) and low lipophilicity (log P ≤ 1.74). In this study we investigate the application of HILIC as a potential alternative approach for the fast separation of the ephedrines phenylpropanolamine, cathine, ephedrine, pseudoephedrine and methylephedrine in doping control analysis. Using sub-2 µm bare silica bridged-ethylene hybrid (BEH) HILIC material, we evaluate the effects of organic modifier, buffer pH and concentration and column temperature on the retention and selectivity of these compounds. Highly symmetrical peak shapes for all ephedrines were achieved under HILIC conditions (A(s0.1) ≤ 1.1). We also compare the kinetic performance of the optimised HILIC separation with a previously developed high pH reversed-phase approach. van Deemter curves and kinetic plots for the two approaches are constructed and illustrate the kinetic benefits of HILIC over the reversed-phase approach. Improved mass transfer characteristics and enhanced diffusion with HILIC offers lower C-term coefficients of 1.46 and 5.68 for ephedrine with HILIC and RPLC, respectively.

Enantiomeric separation of some common controlled stimulants by capillary electrophoresis with contactless conductivity detection.

CE methods with capacitively coupled contactless conductivity detection (C(4)D) were developed for the enantiomeric separation of the following stimulants: amphetamine (AP), methamphetamine (MA), ephedrine (EP), pseudoephedrine (PE), norephedrine (NE) and norpseudoephedrine (NPE). Acetic acid (pH 2.5 and 2.8) was found to be the optimal background electrolyte for the CE-C(4)D system. The chiral selectors, carboxymethyl-ß-cyclodextrin (CMBCD), heptakis(2,6-di-O-methyl)-ß-cyclodextrin (DMBCD) and chiral crown ether (+)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (18C6H(4)), were investigated for their enantioseparation properties in the BGE. The use of either a single or a combination of two chiral selectors was chosen to obtain optimal condition of enantiomeric selectivity. Enantiomeric separation of AP and MA was achieved using the single chiral selector CMBCD and (hydroxypropyl)methyl cellulose (HPMC) as the modifier. A combination of the two chiral selectors, CMBCD and DMBCD and HPMC as the modifier, was required for enantiomeric separation of EP and PE. In addition, a combination of DMBCD and 18C6H(4) was successfully applied for the enantiomeric separation of NE and NPE. The detection limits of the enantiomers were found to be in the range of 2.3-5.7 µmol/L. Good precisions of migration time and peak area were obtained. The developed CE-C(4)D method was successfully applied to urine samples of athletes for the identification of enantiomers of the detected stimulants.

Enantioresolution of five ß-blockers by reversed-phase high-performance liquid chromatography using fifteen chiral derivatizing reagents having amino acids or their amides as chiral auxiliaries on a cyanuric chloride platform.

Enantioseparation of five ß-blockers, namely, (R,S)-atenolol, (R,S)-propranolol, (R,S)-bisoprolol, (R,S)-metoprolol and (R,S)-carvedilol, was achieved as their diastereomers prepared with chiral derivatizing reagents (CDRs) synthesized on a cyanuric chloride platform. Fifteen CDRs were synthesized by nucleophilic substitution of the Cl atom in cyanuric chloride or its 6-methoxy derivative with amino acids (namely, L-Leu, L-Val, D-Phg, L-Met and L-Ala) or their amides as chiral auxiliaries. The diastereomers were synthesized under microwave irradiation for 70 or 100 s at 85% power. Separation of diastereomers was carried out on a C(18) column and gradient eluting mixtures of methanol with aqueous trifluoroacetic acid with UV detection at 230 nm. Separation efficiencies of the reagents were compared on the basis of effect of chiral auxiliaries (i.e. amino acids or amino acid amides) and achiral substituents (i.e. chlorine or methoxy group) in the CDRs. The method was validated for detection limit, linearity, accuracy and precision.