Investigation of Enantiomeric Separation of Chiral Drugs by CE Using Cu(II)–Clindamycin Complex as a Novel Chiral Selector

The enantiomeric separation of several basic drugs was investigated using copper(II)–clindamycin as a new chiral selector. The results show that the chiral selector allows high-resolution separation of some racemic basic drugs, including tropicamide, propranolol, sotalol, bisoprolol, epinephrine, esmolol, atenolol, and metoprolol. The enantioselectivity was influenced by parameters such as the type of metal ion, ratio of clindamycin and Cu(II), pH of the background electrolyte, clindamycin concentration, applied voltage, and capillary temperature. The optimal separation conditions were determined to be 20 mM clindamycin/10 mM Cu²⁺, pH 9.06, at 20 kV and 22 °C within 25 min.

     

The Quantitation of Heroin and Selected Basic Impurities Via Reversed Phase HPLC. I. The Analysis of Unadulterated Heroin Samples

Abstract

Methodology was developed employing reversed phase liquid chromatography for the simultaneous determination of heroin, O³-monoacetylmorphine, o⁶-monoacetylmorphine, acetylcodeine, noscapine and papaverine in unadulterated illicit powders. An HS-5 C18 column was used with a gradient system using methanol and a hexylamine phosphate buffer at pH 2.2. This method, suitable for automated analysis, used a multi-mode detection scheme via the use of a photodiode array detector. In order to arrive at the optimum chromatographic conditions in terms of selectivity and stability, a study was performed on the effect of various mobile phase parameters on log k′ for heroin, various impurities, and common adulterants. The mobile phase parameters included amine concentration, organic modifier type, and eluent pH.     

Synthesis and application of a peroxidase-like molecularly imprinted polymer based on hemin for selective determination of serotonin in blood serum

This work reports the preparation of a molecularly imprinted polymer (MIP) for selective catalytic detection of serotonin (5-hydroxytryptamine, 5-HT). The process is based on the synthesis of polymers with hemin introduced as the catalytic center to mimic the active site of peroxidase. The copolymer MIP, containing artificial recognition sites for 5-HT, has been prepared by bulk polymerization using methacrylic acid (MAA) and hemin as the functional monomers, and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. For the determination of 5-HT, a flow injection analysis system coupled to an amperometric detector was optimized using multivariate analysis. The effects of different parameters, such as pH, buffer flow rate, buffer nature, peroxide concentration and sample volume were evaluated. After optimizing the experimental conditions, a linear response range from 1.0 up to 1000.0 μmol L⁻¹ was obtained with a sensitivity of 0.4 nA/μmol L⁻¹. The detection limit was found to be 0.30 μmol L⁻¹, while the precision values (n = 6) evaluated by relative standard deviation (R.S.D.) were, respectively, 1.3 and 1.7% for solutions of 50 and 750 μmol L⁻¹ of 5-HT. No interference was observed by structurally similar compounds (including epinephrine, dopamine and norepinephrine), thus validating the good performance of the imprinted polymer. The method was applied for the determination of 5-HT in spiked blood serum samples.     

Investigation of Enantiomeric Separation of Chiral Drugs by CE Using Cu(II)�CClindamycin Complex as a Novel Chiral Selector

The enantiomeric separation of several basic drugs was investigated using copper(II)?Cclindamycin as a new chiral selector. The results show that the chiral selector allows high-resolution separation of some racemic basic drugs, including tropicamide, propranolol, sotalol, bisoprolol, epinephrine, esmolol, atenolol, and metoprolol. The enantioselectivity was influenced by parameters such as the type of metal ion, ratio of clindamycin and Cu(II), pH of the background electrolyte, clindamycin concentration, applied voltage, and capillary temperature. The optimal separation conditions were determined to be 20 mM clindamycin/10 mM Cu²⁺, pH 9.06, at 20 kV and 22 °C within 25 min.     

Discontinuous electrolyte systems for improved detection of biologically active amines and acids by capillary electrophoresis with laser-induced native fluorescence detection

On-line concentration and separation of biologically active amines and acids by capillary electrophoresis (CE) in conjunction with laser-induced fluorescence using an Nd:YAG laser at 266 nm under discontinuous conditions is presented. The suitable conditions for simultaneous analysis of amines and acids were: samples were prepared in a solution (pH* 3.1) consisting of 10 mM citric acid, 89% acetonitrile (ACN), and water; a capillary was filled with 1.5 M Tris-borate (TB) buffer (pH 10.0); and the anodic vial contained PTG10 buffer (pH* 9.0) that consists of 50 mM propanoic acid, Tris, 10% glycerol, and water. After injecting a large-volume sample, amines and acids were separately stacked at the front (cathodic side) and back (anodic side) of the acidic sample zone, mainly because of changes in their electrophoretic mobilities as a result of changes in pH, viscosity, and electric field when high voltage was applied. When the sample was injected at 15 kV for 360 s, the concentration limits of detection (LODs) for 5-hydroxytryptamine (5-HT) and 5-hydroxyindole-3-acetic acid (5-HIAA) were 0.27 and 0.31 nM, respectively, which are about 400- and 800-fold sensitivity improvements when compared to those injected at 1 kV for 10 s. For the analysis of amines, samples were prepared in 100 mM citric acid (pH* 1.8) containing 89% ACN and both the capillary and anodic vial were filled with 400 mM PTG20 (propanoic acid, Tris, 20% glycerol, and water) at pH* 4.5. Using a large injection volume (15 kV for 360 s), we achieved concentration LODs of 17 pM and 0.3 nM for tryptamine and epinephrine, which are about 5200- and 14,000-fold sensitivity improvements, respectively, in comparison with those injected at 1 kV for 10 s. The features of simplicity (no sample pretreatment), rapidity (12 min), and sensitivity for identification of amines and acids of interest in urine samples show diagnostic potential of the two approaches developed in this study.     

Spermine-graft-dextran non-covalent copolymer as coating material in separation of basic proteins and neurotransmitters by capillary electrophoresis

Spermine-graft-dextran (Spe-g-Dex) copolymer was synthesized and used as a non-covalent coating for the separation of proteins and neurotransmitters by capillary electrophoresis. The coating was obtained via flushing the capillary with 1.0% Spe-g-Dex copolymer solution for 2 min. Electroosmotic flow (EOF) was strongly suppressed, ranging from −1.60 × 10⁻⁹ to 3.65 × 10⁻⁹ m² V⁻¹ s⁻¹. Effect of experimental conditions, such as the copolymer concentration, the concentration and pH of the background electrolyte (BGE), on the Spe-g-Dex coating was investigated. Separation of lysozyme, cytochrome c, ribonuclease A and α-chymotrypsinogen yielded high separation efficiencies ranging from 141 000 to 303 000 plates/m and recoveries from 85.4% to 98.3% at pH 4.0 (284.0 mM sodium acetate–acetic acid buffer, I = 50 mM). Run-to-run repeatabilities and day-to-day, and capillary-to-capillary reproducibilities were all below 1.7%. In addition, Spe-g-Dex coating allowed the successful separation of five neurotransmitters, 5-hydroxytryptamine, dopamine, epinephrine, isoprenaline, dobuamine at pH 4.0 with high separation efficiencies of 290 000–449 000 plates/m.     

Quantitative Analysts of 5-Hydroxytryptamtne in Biological Material by High Perfornance Liquid Chromatography and Electrochmical Detection

Abstract

A quantitative method for the analysis of 5-hydroxytryptamine in biological material is described. The method is based on high performance liquid chromatography (HPLC) with electrochemical detection. A simple purification on a weakly acidic ion exchange resin prior to the analysis gives quite clean samples and permits concentration of diluted samples. The chromatographic separation is performed on a reverse phase column with organic modifier added to an aqueous eluent. With this analytical system 25 pg of 5-hydroxytryptamine can be detected.     

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM⁻¹, while for epinephrine these values are ~60 nM and 0.19 μA μM⁻¹. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.

     

Ag ion irradiated based sensor for the electrochemical determination of epinephrine and 5-hydroxytryptamine in human biological fluids

A promising and highly sensitive voltammetric method has been developed for the first time for the determination of epinephrine (EP) and 5-hydroxytryptamine (5-HT) using 120 MeV Ag ion irradiated multi-walled carbon nano tube (MWCNT) based sensor. The MWCNT were irradiated at various fluences of 1e12, 3e12 and 1e13 ions cm⁻² using palletron accelerator. The simultaneous determination of EP and 5-HT has been carried out in phosphate buffer solution of pH 7.20 using square wave voltammetry and cyclic voltammetry. Experimental results suggested that irradiation of MWCNT by Ag ions enhanced the electrocatalytic activity due to increase in effective surface area and insertion of Ag ions, leading to a remarkable enhancement in peak currents and shift of peak potentials to less positive values as compared to the unirradiated MWCNT (pristine). The developed sensor exhibited a linear relationship between peak current and concentration of EP and 5-HT in the range 0.1–105 μM with detection limit (3σ/b) of 2 nM and 0.75 nM, respectively. The practical utility of irradiation based MWCNT sensor has been demonstrated for the determination of EP and 5-HT in human urine and blood samples.     

Preparing of Iridium Oxide Film Modified Microelectrode as an Amperometric Detector in FIA for Determination of Epinephrine

Abstract

Iridium oxide film modified microelectrode with a tip diameter of 25 µm was constructed using anodically grown iridium oxide film. The iridium oxide film, which was formed at the tip of the iridium wire by cyclic voltammetry in dilute sulfuric acid, showed excellent catalytic activity towards the oxidation of epinephrine. The stability and electrochemical properties of iridium oxide film modified microelectrode along with catalytic oxidation of epinephrine was studied. An oxidation peak was observed at 0.28 V. The electron‐transfer number (n) was 2. The iridium oxide film modified microelectrode was used as a detector in flow injection system for determination of epinephrine. Under the optimized conditions, the calibration curve was linear in the concentration range of 1.0×10^?8 to 1.0×10^?5 mol/l for epinephrine, with a detection limit of 1.0×10^?9 mol/l. The iridium oxide film modified microelectrode was used for direct determination of the epinephrine in human serum samples. The flow injection analysis was precise detection method of epinephrine and time saving device.     

Effect of Salt and pH on the Hydrophobicity of Some Basic Ion-Pairing Agents

Abstract

The lipophilicity (hydrophobicity) of some alkyl and arylamines was determined with reversed-phase thin-layer chromatography using water:methanol 1:1 v/v eluent with salt and various buffers added to the system. The effect of various structural parameters of amines and that of the chromatographic conditions were assessed with stepwise regression analysis. Both salt concentration and pH influenced the lipophilicity of amines decreasing linearly with increasing salt concentration and pH. The lipophilicity values of alkylamines extrapolated to 0 pH showed a very low dependence on the length of alkyl chain. The PH sensitivity of alkylnmines depended linearly on the length of alkyl chain.     

Contribution à l'étude Électrochimique de Dérivés de l'Acide Mercapto-2 Pyridinecarboxylique-5. II

Abstract

Electrochemical caracteristics of 2-mercaptopyridine-5-carboxylic acid and its methylic ester have been determined using recent polarographic techniques. Measurements have been carried out as a function of parameters such as frequency, others surimposed signals and as a function of concentration and pH. Results are compared to those obtained for selectively methylated on sulfur or nitrogen atoms derivatives. Interpretations of the data are given. The optimal conditions for a quantitative determination by D.C. and differential pulse polarography are fixed.     

Hollow-Fiber-Based LPME as a Reliable Sampling Method for Gas-Chromatographic Determination of Pharmacokinetic Parameters of Valproic Acid in Rat Plasma

A sensitive and simple method based on two-phase liquid-phase microextraction in porous hollow fiber followed by gas chromatography-flame ionization detection was developed for quantification and pharmacokinetic study of valproic acid (VPA, an antiepileptic drug) in rat plasma after oral administration of pure sodium valproate (25 mg kg⁻¹). Some parameters such as type of organic solvent, pH of sample solution, stirring speed, salt addition, extraction time, and volume of sample that affected extraction efficiency of VPA were optimized. Under optimized microextraction conditions, VPA was extracted with 10 μL 1-octanol from 0.5 mL rat plasma previously diluted with 4.5 mL acidified and salinated water (pH 2) using 1-octanoic acid as internal standard. The limit of detection was 17 ng mL⁻¹ with linear response over the concentration range of 50–10,000 ng mL⁻¹ with correlation coefficient higher than 0.998. The developed method was successfully applied to determination of pharmacokinetic parameters such as t _max (peak time in concentration–time profile), C _max (peak concentration in concentration–time profile), t _1/2 (elimination half-life), AUC_0–t (area under the curve for concentration versus time), clearance, and apparent distribution volume in rats following oral administration of VPA.

     

CE‐LIF chiral separation of aspartic acid and glutamic acid enantiomers using human serum albumin and sodium cholate as dual selectors

Sodium cholate (SC), β‐CD, hydroxypropyl (HP)‐β‐CD, HSA, and the dual mixtures of them were evaluated for the analysis of aspartic acid (Asp) and glutamic acid (Glu) enantiomers fluorescently tagged with 5‐(4,6‐dichloro‐s‐triazin‐2‐ylamino) fluorescein (DTAF) by CE with LIF detection. Among the investigated chiral selectors and the dual selector systems, the dual selector systems of HSA and SC resulted to be the most useful chiral selectors allowing relatively high chiral resolution. Several experimental parameters such as chiral reagent type and concentration, buffer concentration, and pH, type and concentration of organic modifier were studied in order to find the optimum conditions for the chiral resolution of the two derivatized amino acids in their enantiomers. The effect of different variables that affect derivatization (time, temperature, pH, and DTAF concentration) was studied. Under optimum conditions, the analytes were separated in a short 10.5 min analysis time, and the RSDs for migration time and peak area were less than 0.12 and 2.8%, respectively. The method was applied for the analysis of compound amino acids injection without interference from other amino acids in the sample matrices observed.     

Optimization of CuW alloy electrodeposition towards high-tungsten content

With the help of the factorial design of experiments, optimization of the deposition of the CuW alloy was successfully done. The important deposition parameters were identified as pH, current density, and—the most important one—copper ion concentration. All of them were examined in their wide ranges. Under optimal conditions, in a citrate bath, with copper ion concentration of 1.0 mM, at current density of −100 mA cm⁻² and at pH ca. 8.3, the alloy layer had the highest tungsten content (circa 30 wt.%), satisfactory adhesion and a smooth and crackless morphology. The structure of the electrodeposited alloy can be described as an amorphous solid solution of Cu in W with built-in Cu nanocrystals.

     

Adsorptive Stripping Square-Wave Voltammetry of Creatine

ABSTRACT

An adsorptive stripping square-wave voltammetric method for quantitative determination of creatine is developed. The basic redox properties of creatine are investigated by means of square-wave and cyclic staircase voltammetry. Creatine undergoes an irreversible reduction in neutral and acidic medium at a hanging mercury drop electrode. The square-wave voltammetric response of creatine depends on the parameters of the SW excitation signal as well as on the concentration and type of the supporting electrolyte, the accumulation time and the potential and pH of the medium. The optimal experimental conditions for quantitative determination of creatine are as follows: supporting electrolyte 0.1 mol/L KNO₃ buffered with 0.1 mol/L acetate buffer to pH = 4 and accumulation potential -1.2 V. The optimal SW parameters found are: frequency f = 120 Hz, amplitude E _sw = 30 mV, and scan increment dE = 4 mV. A detection limit of 6.6 x 10^?8 mol/L creatine was obtained after 30 s preconcentration period at accumulation potential -1.2 V. The correlation coefficients of the calibration curves at concentration levels of 10^?7 to 10^?5 mol/L creatine are greater than 0.99. The results of recovery tests range from 92.18% to 102.51%.     

In vivo monitoring of the monoamine neurotransmitters in the rat brain by microdialysis coupled with the liquid chromatography dual electrochemical detector

The carbon film based ring-disk dual electrodes in the thin-layer radial flow cell are used as the dual electrochemical detector (DECD) for liquid chromatography (LC) to determine the monoamine neurotransmitters. Cyclic voltammetric experiments show there has great difference in the reversibility of the oxidative reactions of dopamine and ascorbate. Therefore the ring-disk dual electrode arrangement in the radial flow cell can effectively remove the interference of ascorbate and determine dopamine in the LC-DECD. In order to obtain the better collection efficiency (CE) and better peak current of analytes in the LC-DECD, several operational parameters have been investigated: flow rate, pH and the working potentials. Under the optimum conditions, the method shows a good stability and reproducibility to determine dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT), epinephrine (E) and 3,4-dihydroxyphenylacetic acid (DOPAC). The limits of detection are 0.1 pmol for DA, 0.1 pmol for NE, 0.1 pmol for 5-HT, 1.0 pmol for E and 0.1 pmol for DOPAC. The application of this method, coupled with microdialysis sampling, for the in vivo determination of the monoamine neurotransmitters in the striatum of the rat brain is satisfactory.     

Synthesis and properties of lignin peroxidase fromstreptomyces viridosporus T7A

The production of lignin peroxidase byStreptomyces viridosporus T7A was studied in shake flasks and under aerobic conditions in a 7.5-L batch fermentor. Lignin peroxidase synthesis was found to be strongly affected by catabolite repression. Lignin peroxidase was a non-growth-associated, secondary metabolite. The maximum lignin peroxidase activity was 0.064 U/mL at 36 h.

In order to maximize lignin peroxidase activity, optimal conditions were determined. The optimal incubation temperature, pH, and substrate (2,4-dichlorophenol) concentration for the enzyme assays were 45°C, 6, and 3 mM, respectively. Stability of lignin peroxidase was determined at 37, 45, and 60°C, and over the pH range 4–9.

     

Liquid–Liquid Microextraction of Nitrophenols Using Supramolecular Solvent and Their Determination by HPLC with UV Detection

A novel, efficient, and environmentally friendly method—supramolecular solvent liquid–liquid microextraction (SMS-LLME) combined with high-performance liquid chromatography (HPLC)—was first established for the determination of p-nitrophenol and o-nitrophenol in water samples. Several important parameters influencing extraction efficiency, such as the type and volume of extraction solvent, pH of sample, temperature, salt effect, extraction time, and stirring rate, were optimized in detail. Under the optimal conditions, the enrichment factor was 166 for p-nitrophenol and 160 for o-nitrophenol, and the limits of detection by HPLC were 0.26 and 0.58 μg L⁻¹, respectively. Excellent linearity with coefficients of correlation from 0.9996 to 0.9997 was observed in the concentration range of 2–1,000 μg L⁻¹. The ranges of intra- and interday precision (n = 5) at 100 μg L⁻¹ of nitrophenols were 5.85–7.76 and 10.2–11.9 %, respectively. The SMS-LLME method was successfully applied for preconcentration of nitrophenols in environmental water samples.

     

Chiral Separation of Ketoprofen on a Chirobiotic T Column and Its Chiral Recognition Mechanisms

Purpose

In this study, direct separation of ketoprofen enantiomers was performed on a Chirobiotic T column.

Methods

The effects of the type and amount of the organic modifier, buffer concentration, pH value, temperature and flow rate on retention and selectivity were investigated. Experiments were carried out in the temperature range of 20–40 °C to study the effects of temperature. Thermodynamic parameters were calculated from plots of ln k or ln α versus 1/T. Molecular dynamics simulation was done to investigate interactions between ketoprofen enantiomers and the chiral selector—teicoplanin.

Results

It was observed that pH and flow rate had a large influence on resolution. Baseline separation of ketoprofen enantiomers could be achieved with low amounts of methanol, high temperature and high buffer concentrations.

Conclusions

Results from a thermodynamic study and molecular dynamics simulation show that steric hindrance effect, π–π complexation, hydrogen bonding and electrostatic forces are the main driving forces which cause chiral recognition of ketoprofen enantiomers.