bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mesoporous Materials Promoting Direct Electrochemistry and Electrocatalysis of Horseradish Peroxidase
Authors: Dai Zhihui , Ju Huangxian , Chen Hongyuan 
Published: February 2005

AbstractThe direct electron transfer and electrocatalysis of horseradish peroxidase (HRP) immobilized on hexagonal mesoporous silicas (HMS) matrix was studied. The interaction between HRP and HMS was examined by using Fourier transform infrared spectroscopy, nitrogen adsorption isotherms and electrochemical methods. The immobilized HRP at a modified glassy carbon electrode showed a good direct electrochemical behavior, which depended on the specific properties of the HMS. Two couples of redox peaks corresponding to Fe(III) to Fe(II) conversion of the HRP intercalated in the mesopores and adsorbed on the external surface of the HMS were observed with the formal potentials of −0.315 and −0.161 V in 0.1 M pH 7.0 PBS, respectively. The amount of HRP intercalated in the mesopores of HMS proved to be related to the pore size. The HRP intercalated in the mesopores showed a surface controlled electrode process with a single proton transfer. The immobilized HRP displayed an excellent electrocatalytic response to the reduction of hydrogen peroxide (H2O2) without the aid of an electron mediator. The HMS provided a novel matrix for protein immobilization and direct electron transfer study of the immobilized protein.
Separation and determination of L‐tryptophan and its metabolites by capillary micellar electrokinetic chromatography with amperometric detection
Authors: Wang Wei , Qiu Bin , Xu Xueqin , Zhang Lan , Chen Guonan 
Published: February 2005

AbstractA high‐performance method of capillary micellar electrokinetic chromatography (CMEKC) with amperometric detection (AD), using a newly designed pre‐aligned electrochemical cell, has been developed for the separation and determination of L‐tryptophan (Trp) and its eight metabolites including 3‐hydroxy‐L‐kynurenine (3‐HK), 5‐hydroxy‐L‐tryptophan (5‐HTP), L‐kynurenine (KN), 5‐hydroxyindole‐3‐acetic acid (5‐HIAA), xanthurenic acid (XA), indole‐3‐pyruvic acid (IPA), 5‐hydroxytryptamine (5‐HT), and tryptamine (Tryp). A carbon disk electrode was used as the working electrode and the optimal detection potential was 0.85 V (versus Ag/AgCl). At 24 kV of applied voltage, the nine compounds were completely separated, within 23 min, in a 10 mol/L Na2HPO4‐NaOH buffer (pH 11.0) containing 40 mmol/L sodium dodecyl sulfate (SDS) and 3% methanol (v/v). A good linear relationship was obtained for all analytes in this paper and the detection limits of 3‐HK, 5‐HTP, KN, Trp, 5‐HIAA, XA, IPA, 5‐HT, and Tryp were 7.42, 5.18, 34.6, 3.99, 15.1, 12.7, 260, 6.72, and 8.01 nmol/L, respectively. This method has been applied to analyze the metabolism of Trp in rabbit urine.
Chiral separation based on ligand‐exchange capillary electrophoresis using a copper(II)‐L‐ornithine ternary complex as selector
Authors: Zheng Zhi‐Xia , Wei Yanlin , Lin Jin‐Ming 
Published: February 2005

AbstractA 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 104 to 105. 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.
Micellar proportion: A parameter to compare the hydrophobicity of the pseudostationary phases or that of the analytes in micellar electrokinetic chromatography
Authors: Dobos Zsófia , Kiss Éva , Hallgas Balázs , Kéri György , Idei Miklós 
Published: February 2005

AbstractMicellar proportion, tprop,mic = tmic/tm, a quantity expressing how much time is spent by the analyte in the micellar phase related to its whole migration time (tm) has been introduced by utilizing the micellar phase residence time (tmic). The tprop,mic values have been determined for analytes of different chemical structures (alkyl benzene and alkyl phenone homologous series, alcohols, strongly hydrophobic peptides) studied by micellar elektrokinetic chromatography (MEKC) using various cationic and anionic pseudostationary phases. A good linear correlation was obtained between tprop,mic and the calculated hydrophobicity (CLOGP) of the analytes for all pseudostationary phases (CLOGP = A·logtprop,mic + B). Considering a given pseudostationary phase, tprop,mic as a relative quantity is a suitable parameter to characterize and compare experimentally the behavior of the various analytes in MEKC. Applying a set of probe molecules with known hydrophobicity, the CLOGP50 value (showing the value of hydrophobicity of a virtual molecule spending exactly 50% of its migration time in the pseudostationary phase) has been calculated for each pseudostationary phase applied here. This experimentally determinable numerical value (characterizing the pseudostationary phase) can be utilized to compare the hydrophobicity and hence retention ability of the pseudostationary phases. The tprop,mic value was found to be applicable to compare the methylene selectivity of the different pseudostationary phases as well: logtprop,mic = A·Z + B, where Z is the number of carbon atoms of the alkyl chain in the alkyl benzene homologous series.
Analysis of anticancer platinum(II)‐complexes by microemulsion electrokinetic chromatography: Separation of diastereomers and estimation of octanol‐water partition coefficients
Authors: Rappel Christina , Galanski Mathea Sophia , Yasemi Afshin , Habala Ladislav , Keppler Bernhard K. 
Published: February 2005

AbstractMicroemulsion electrokinetic chromatography (MEEKC) was applied for the separation and lipophilicity estimation of oxaliplatin and eight novel anticancer oxaliplatin derivatives. Solubility and permeability have to be balanced in modern drug development, and the octanol‐water partition coefficient (log P) still represents one of the most useful quantifiable parameters providing a reasonable estimation of a drug's lipophilicity. Therefore, the capacity factors from MEEKC were correlated to log P values derived by the traditional shake flask method. The MEEKC method was accomplished using a microemulsion of heptane/sodium dodecyl sulfate (SDS)/butanol in phosphate buffer at pH 7.4 and 37°C with all analytes being in a neutral state during the run. This experimental setup allowed a baseline separation of all platinum complexes within 11 min. Remarkably, beside the very good resolution and precision of the measurements, separation of diastereomers of the complexes and quantification of the diastereomeric ratios could be achieved. Correlating the capacity factors with the corresponding log P values resulted in a linear dependency with a correlation factor of r = 0.9935. Consequently, the applied MEEKC method was found to be a highly valuable technique not only for the separation of platinum complexes but as well for the estimation of the octanol‐water partition coefficient with many advantages in comparison to other methods.
On‐column capillary electrophoretic monitoring of rapid reaction kinetics for determination of the antioxidative potential of various bioactive phenols
Authors: Vaher Merike , Ehala Sille , Kaljurand Mihkel 
Published: February 2005

AbstractAn on‐column capillary electrophoretic procedure for the determination of the antioxidative potential of various bioactive phenols, found in plant, fruit, and vegetable extracts, is described. The assay is based on a rapid mixing of phenols or phenolic extracts before the capillary, followed by pressurized injection of the reaction mixture into the capillary. After incubation of the reaction mixture inside the capillary, high voltage is switched on and separation of reactants and products is performed. Using hydrogen peroxide as a stressor, the kinetics of the oxidation of various bioactive phenols was studied (rutin, chlorogenic acid, quercetin, caffeic acid, gallic acid, and combinations of these) and compared with the oxidation rate of L‐ascorbic acid as a reference. The concept was demonstrated for the determination of the antioxidative potential of various polyphenol mixtures and of the methanol extract of the sea buckthorn (Hippophaë rhamnoides L.). In most cases quercetin has the highest rate constant of oxidation among the tested phenolic compounds. However, in the mixture L‐ascorbic acid/quercetin, the oxidation rate of L‐ascorbic acid was enhanced and oxidation of quercetin was strongly inhibited compared with the other combinations of tested polyphenols.
Comparison of microemulsion electrokinetic chromatography and micellar electrokinetic chromatography as methods for the analysis of ten benzophenones
Authors: Huang Hsi‐Ya , Chiu Chen‐Wen , Chen Yen‐Chen , Yeh Jui‐Ming 
Published: February 2005

AbstractMicroemulsion electrokinetic chromatography (MEEKC) and micellar electrokinetic chromatograpy (MEKC) were compared for their abilities to separate and detect ten similar benzophenones, which are commonly used as UV filters in various plastic and cosmetic products. Sodium dodecyl sulfate (SDS) concentration and column temperature rarely affected separation resolution for MEEKC, but separation of benzophenones could be improved by changing the SDS concentration and column temperature for MEKC. Buffer pH and ethanol (organic modifier) were found to markedly influence the separation selectivity for both MEEKC and MEKC systems. In addition, a higher electric voltage improved the separation efficiency without a noticeable reduction in separation resolution for MEEKC, whereas it caused a poor separation resolution for the MEKC system.
Electrokinetic capillary chromatography in a polar continuous‐phase water‐in‐oil microemulsion constituted by water, sodium dodecyl sulfate, and n‐pentanol
Authors: Mendonça Carla R. B. , Bica Clara I. D. , Piatnicki Clarisse M. S. , Simó‐Alfonso Ernesto F. , Ramis‐Ramos Guillermo 
Published: February 2005

AbstractA water‐in‐oil (w/o) microemulsion (ME) constituted by 15% Tris buffer, pH 8.4, in water and 85% sodium dodecyl sulfate (SDS)/n‐pentanol 1:4 mixture, capable of dissolving up to 30% vegetable oils and lard, was used as background electrolyte in reverse microemulsion electrokinetic capillary chromatography (RMEEKC). Owing to the free SDS ions in the continuous phase and some degree of percolation, the ME showed a high conductivity (0.65 mS· cm‐1 at 25°C) and sustained a very stable capillary current. Previous rinsing of the capillary with a quaternary ammonium salt for electroosmotic flow (EOF) reduction, a series of nonionic and anionic solutes dissolved either in the ME or in fat samples diluted with the ME (1:4 ratio), were injected. Using −20 kV, fair separations of the solutes in the migration time order singly charged anions < nonionic solutes < doubly charged anions ∼ pyromellitate were obtained, salicylate (I) showing by far the shortest migration time, and phthalate (II) and pyromellitate the longest. Separation was attributed to partition between the aqueous droplets, where pyromellitate and II were assumed to be trapped, and the n‐pentanol continuous phase, where the mobilitites could be also modified by association of the solutes with SDS ions. Adequate EOF markers were not found, thus the relative mobility of any solute with respect to the mobility of the droplets, μr, was expressed as a fraction of the mobility of I with respect to that of the droplets, being μr = (tII − tR) tI / [(tII − tI) tR], where tR, tI, and tII are the migration times of the solutes I and II, respectively. The application of RMEEKC to the analysis of both hydrophilic and hydrophobic samples, including edible fats, was demonstrated.
Rapid assessment of β‐asarone content of Acorus calamus by micellar electrokinetic capillary chromatography
Authors: Hanson Kim M. , Gayton‐Ely Melissa , Holland Lisa A. , Zehr Peter S. , Söderberg Björn C. G. 
Published: February 2005

AbstractThis report outlines a rapid, reproducible method for the determination of β‐asarone, a known carcinogen, using micellar electrokinetic capillary chromatography (MEKC)‐UV‐vis absorbance and a simple alcohol extraction. The MEKC method is based on a running buffer comprised of 100 mM sodium dodecyl sulfate (SDS), pH 10. The method is reproducible and provides baseline separation of α‐asarone and β‐asarone. This protocol was used to determine the β‐asarone content of Acorus calamus rhizome of a diploid variety harvested from the wetlands of the United States and the triploid variety from India obtained commercially. The results indicate raw product that originated from India contained 4.4% w/w β‐asarone, while that from the United States contained 0.2% w/w β‐asarone. Neither sample contained detectable concentrations of α‐asarone. This is the first report of the use of MEKC to determine asarone in a natural source.
Determination of ceftazidime in plasma and cerebrospinal fluid by micellar electrokinetic chromatography with direct sample injection
Authors: Yeh Hsin‐Hua , Yang Yuan‐Han , Chou Yu‐Wei , Ko Ju‐Yun , Chou Chia‐An , Chen Su‐Hwei 
Published: February 2005

AbstractA simple micellar electrokinetic chromatography (MEKC) with UV detection at 254 nm for analysis of ceftazidime in plasma and in cerebrospinal fluid (CSF) by direct injection without any sample pretreatment is described. The separation of ceftazidime from biological matrix was performed at 25°C using a background electrolyte consisting of Tris buffer with sodium dodecyl sulfate (SDS) as the electrolyte solution. Under optimal MEKC condition, good separation with high efficiency and short analyses time is achieved. Several parameters affecting the separation of the drug from biological matrix were studied, including pH and concentration of the Tris buffer and SDS. Using cefazolin as an internal standard (IS), the linear ranges of the method for the determination of ceftazidime in plasma and in CSF were all over the range of 3–90 μg/mL; the detection limit of the drug in plasma and in CSF (signal‐to‐noise ratio = 3; injection 0.5 psi, 5 s) was 2.0 μg/mL. The applicability of the proposed method for determination of ceftazidime in plasma and CSF collected after intravenous administration of 2 g ceftazidime in patients with meningitis was demonstrated.
Separation strategy for acidic chiral pharmaceuticals with capillary electrochromatography on polysaccharide stationary phases
Authors: Mangelings Debby , Tanret Indiana , Matthijs Nele , Maftouh Mohamed , Massart D. Luc , Vander Heyden Yvan 
Published: February 2005

AbstractThe effect of five factors on the capillary electrochromatographic enantioseparation of acidic compounds was studied using an experimental design. The studied factors were pH, acetonitrile content in the mobile phase, temperature, buffer concentration, and applied voltage. These experiments allowed defining a generic separation strategy applicable on acidic compounds with chemical and structural diversity. The starting screening conditions consist of a 45 mM ammonium formate electrolyte at pH 2.9 mixed with 65% acetonitrile, an applied voltage of 15 kV, and a temperature of 25°C. The screening phase occasionally can be followed by an optimization procedure. Evaluation of the proposed strategy pointed out that it allows achieving baseline resolution within a relatively short time when a beginning of separation is obtained at the starting conditions. This strategy revealed enantioselectivity for 11 compounds out of 15, of which 10 could be baseline‐separated after the proposed optimization steps.
Recent advances in micellar electrokinetic chromatography
Authors: Pappas Theron J. , Gayton‐Ely Melissa , Holland Lisa A. 
Published: February 2005

AbstractThis review contains nearly 200 reference citations, and covers advances in electrokinetic capillary chromatography based on micelles, including stabilized micelle complexes, polymeric and mixed micelles from 2003–2004. Detection strategies, analyte determinations, and applications in micellar electrokinetic capillary chromatography (MEKC) are discussed. Information regarding methods of analyte concentration, analyte specific analyses, and nonstandard micelles has been summarized in tabular form to provide a means of rapid access to information pertinent to the reader.
Conformational effects on the performance and selectivity of a polymeric pseudostationary phase in electrokinetic chromatography
Authors: McCarney Jonathan P. , Loflin Robert D. , Rauk Erika , Yusa Shin‐Ichi , Palmer Christopher P. 
Published: February 2005

AbstractThe effect of the conformation of a polymeric pseudostationary phase on performance and selectivity in electrokinetic chromatography was studied using an amphiphilic pH‐responsive polymer that forms compact intramolecular aggregates (unimer micelles) at low pH and a more open conformation at high pH. The change in conformation was found to affect the electrophoretic mobility, retention, selectivity, and separation efficiency. The low‐pH conformer has higher electrophoretic mobility and greater affinity for most solutes. The unimer micelle conformation was also found to provide a solvation environment more like that of micelles and other amphiphilic self‐associative polymers studied previously. It was not possible to fully characterize the effect of conformation on efficiency, but very hydrophobic solutes with long alkyl chains appeared to migrate with better efficiency when the unimer micelle conformation was employed. The results imply that polymers with a carefully optimized lipophilic‐hydrophilic balance that allow self‐association will perform better as pseudostationary phases. In addition, the results show that electrokinetic chromatography is a useful method for determining the changes in solvation environment provided by stimuli‐responsive polymers with changes in the conditions.
Analysis of antiepileptic drugs in biological fluids by means of electrokinetic chromatography
Authors: Pucci Vincenzo , Raggi Maria Augusta 
Published: February 2005

AbstractAn overview of the electrokinetic chromatographic methods for the analysis of antiepileptic drug levels in biological samples is presented. In particular, micellar electrokinetic capillary chromatography is a very suitable method for the determination of these drugs, because it allows a rapid, selective, and accurate analysis. In addition to the electrokinetic chromatographic studies on the determination of antiepileptic drugs, some information regarding sample pretreatment will also be reported: this is a critical step when the analysis of biological fluids is concerned. The electrokinetic chromatographic methods for the determination of recent antiepileptic drugs (e.g., lamotrigine, levetiracetam) and classical anticonvulsants (e.g., carbamazepine, phenytoin, ethosuximide, valproic acid) will be discussed in depth, and their pharmacological profiles will be briefly described as well.
Micellar electrokinetic chromatography of bilirubin, related compounds, and selected drugs with mixtures of binary bile salts
Authors: Olivares Juan , Conner Matthew J. , Vass Christa A. , Kurtin William. E. , Bushey Michelle M. 
Published: February 2005

AbstractMicellar electrokinetic chromatography was used to study the behavior of quinine, propranolol, bilirubin, biliverdin dimethyl ester, and xanthobilirubin methyl ester in single and binary bile salt micelle systems comprised of glycocholic acid and glycodeoxycholic acid. Micelle systems studied had total bile salt concentrations in the range of 10–33 mM with molar ratios of 1:0, 2:1, 1:1, 1:2, and 0:1 glycocholic acid:glycodeoxycholic acid. A pH 8.5 phosphate‐borate buffer system was used. For all analytes except bilirubin, the smallest migration factors were found in glycocholic acid solutions and the largest in glycodeoxycholic acid solutions. Intermediate migration factors were found for all compounds except bilirubin in the binary bile salt systems. Bilirubin behaved uniquely with its largest migration factors in the binary bile salt mixtures.
Investigation of the stability of polyelectrolyte multilayer coatings in open‐tubular capillary electrochromatography using laser scanning confocal microscopy
Authors: Kapnissi‐Christodoulou Constantina P. , Lowry Mark , Agbaria Rezik A. , Geng Lei , Warner Isiah M. 
Published: February 2005

AbstractA simple polyelectrolyte multilayer (PEM) coating procedure was used for the development of stable modified capillaries. PEM coatings were constructed in fused‐silica capillaries using alternating rinses of cationic and anionic polyelectrolytes. The multilayer coatings investigated in this study consisted of two and twenty layer pairs, or bilayers. A bilayer is one layer of a cationic polymer and one layer of an anionic polymer. Poly(diallyldimethylammonium chloride) was used as the cationic polymer, and the polymeric surfactant poly(sodium N‐undecanoyl‐L‐leucylvalinate) was used as the anionic polymer. Previous studies for both chiral and achiral separations have shown that PEM‐coated capillaries have excellent reproducibilities, remarkable endurance, and strong stabilities against extreme pH values when used in open‐tubular capillary electrochromatography (OT‐CEC). In this study, the stability of the coatings was further investigated after exposure to 0.1 M and 1.0 M NaOH. Structural changes of these coatings were monitored using laser scanning confocal microscopy (LSCM) after flushing the capillaries with NaOH. This technique allowed observation of the degradation of the coatings. Observations are discussed in terms of separations using OT‐CEC. Electropherograms obtained from the chiral separation of 1,1'‐binaphthyl‐2,2'‐dihydrogenphosphate in OT‐CEC showed a decrease in selectivity and an increase in electroosmotic mobility after long exposure to NaOH. The ability to recover the capillaries by exposure to NaOH was also demonstrated. Measurements of electroosmotic mobility and selectivity showed that 2‐bilayer and 20‐bilayer PEM coatings could be completely removed from the capillary surface after approximately 3.5 and 9.5 h, respectively, of continuous exposure to 1 M NaOH.
Lipid vesicles in capillary electrophoretic techniques: Characterization of structural properties and associated membrane‐molecule interactions
Authors: Owen Rebecca L. , Strasters Joost K. , Breyer Emelita D. 
Published: February 2005

AbstractThis paper reviews the use of lipid vesicles as model membranes in capillary electrophoresis (CE). The history and utility of CE in the characterization of microparticles is summarized, focusing on the application of colloidal electromigration theories to lipid vesicles. For instance, CE experiments have been used to characterize the size, surface properties, enclosed volumes, and electrophoretic mobilities of lipid vesicles and of lipoprotein particles. Several techniques involving small molecules or macromolecules separated in the presence of lipid vesicles are discussed. Interactions between the analytes and the lipid vesicles – acting as a pseudostationary phase or coated stationary phase in electrokinetic chromatography (EKC) – can be used to obtain additional information on the characteristics of the vesicles and analytes, and to study the biophysical properties of membrane‐molecule interactions in lipid vesicles and lipoproteins. Different methods of determining binding constants by EKC are reviewed, along with the relevant binding constant calculations and a discussion of the application and limitations of these techniques as they apply to lipid vesicle systems.