bluuebunny/crossref_metadata_2025_split huggingface dataset:
Co‐electroosmotic capillary electrophoresis determination of phenolic acids in commercial olive oil
Authors: Carrasco Pancorbo Alegría , Segura Carretero Antonio , Fernández Gutiérrez Alberto 
Published: May 2005

AbstractFourteen phenolic acids have been selectively determined in olive‐oil samples using the co‐electrosmotic capillary electrophoresis mode with UV detection after the LLE extraction system. A polycationic surfactant (hexadimetrine bromide, HDB), which dynamically coats the inner surface of the capillary and causes a fast anodic electroosmotic flow, was added to the electrolyte. The main factors affecting co‐electroosmotic flow (EOF) such as type of modifier, concentration, and influence of organic solvents have been studied. Other parameters such as pH, type, and concentration of buffer, applied voltage, and injection time were also optimised using hydrodynamic injection for 8 s and UV detection at 210 nm. The composition optimum of the running buffer used was a 20% 2‐propanol, 0.001% HDB, and 50 mM sodium borate at a pH value of 9.6. The method has been applied to determination and quantification of fourteen phenolic acids at ppb levels in olive oil samples after a liquid‐liquid extraction.
Identification of character‐impact odorants in coriander and wild coriander leaves using gas chromatography‐olfactometry (GCO) and comprehensive two‐dimensional gas chromatography–time‐of‐flight mass spectrometry (GC×GC–TOFMS)
Authors: Eyres Graham , Dufour Jean‐Pierre , Hallifax Gabrielle , Sotheeswaran Subramaniam , Marriott Philip J. 
Published: May 2005

AbstractThe essential oil of coriander leaves (Coriandrum sativum) and wild coriander leaves (Eryngium foetidum) grown in Fiji was obtained by steam distillation. The aroma profiles were characterised using gas chromatography‐olfactometry (GCO) and CharmAnalysisTM. The character‐impact odorants were identified using comprehensive two‐dimensional gas chromatography (GC×GC) combined with time‐of‐flight mass spectrometry (TOFMS). During GCO analysis, the co‐elution of E‐2‐alkenals and E‐2‐alken‐1‐ols resulted in the perception of ‘odour‐clusters’. The most important odorants in C. sativum were found to be Z‐2‐decenal, a co‐eluting odour‐cluster (E‐2‐dodecenal, E‐2‐dodecen‐1‐ol, and 1‐dodecanol), β‐ionone, eugenol, and E‐2‐decenal. E‐2‐Decen‐1‐ol was the most abundant compound in C. sativum (26.0% TIC) but only contributed 0.39% of the total odour activity. The most abundant compound in E. foetidum was E‐2‐dodecenal (63.5% TIC), which also contributed the most odour activity (52.9%). Other important odorants were either eugenol or a trimethylbenzaldehyde isomer, β‐ionone, Z‐4‐dodecenal, dodecanal, and E‐2‐tetradecenal. GC×GC–TOFMS allowed the identification of 42 and 20 compounds not previously reported in the literature for C. sativum and E. foetidum, respectively. In particular, β‐ionone was determined to be an important odorant in both samples but could not be identified with GC–qMS.
Development of a method for quantitative analysis of the major whey proteins by capillary electrophoresis with on‐capillary derivatization and laser‐induced fluorescence detection
Authors: Veledo María Teresa , de Frutos Mercedes , Diez‐Masa José Carlos 
Published: May 2005

AbstractThe main whey proteins have been derivatized on‐capillary with 3‐(2‐furoyl)quinoline‐2‐carboxaldehyde (FQ) and analyzed using a laboratory‐made capillary electrophoresis apparatus provided with a laser‐induced fluorescence detector. Several parameters controlling on‐capillary derivatization of proteins, including pH, mixing time, reaction time, concentration of the reagents (potassium cyanide and FQ), and reaction temperature, were optimized. Coefficient variations were lower than 1% for migration time and 7% for peak height. Assay detection limits for the different proteins were in the range 5 nM to 10 nM. The method developed was applied to the separation of the major whey proteins in a laboratory‐made cheese whey and in an infant food formulated with milk. In addition, the β‐LG content of these samples was quantitated. The results showed good agreement with those given by an RP‐HPLC method and with those reported in the literature.
Optimization of a multi‐residue screening method for the determination of 85 pesticides in selected food matrices by stir bar sorptive extraction and thermal desorption GC‐MS
Authors: Ochiai Nobuo , Sasamoto Kikuo , Kanda Hirooki , Yamagami Takashi , David Frank , Tienpont Bart , Sandra Pat 
Published: May 2005

AbstractA multi‐residue method to determine 85 pesticides, including organochlorine pesticides, carbamates, organophosphorus pesticides, and pyrethroids, in vegetables, fruit, and green tea, has been developed. The method is based on stir bar sorptive extraction (SBSE) coupled to thermal desorption (TD) and retention time locked (RTL) GC‐MS operating in the scan mode. Samples are extracted with methanol and diluted with water prior to SBSE. Dilution of the methanol extract before SBSE was optimized to obtain high sensitivity and to minimize adsorption onto the glass wall of the extraction vessel as well as to minimize sample matrix effects (particularly for the pesticides with high log Ko/w values). The optimized method consists of a dual SBSE extraction performed simultaneously on respectively a twofold and a fivefold diluted methanol extract. After extraction, the two stir bars are placed in a single glass thermal desorption liner and are simultaneously desorbed. The method showed good linearity (r 2 > 0.9900) and high sensitivity (limit of detection: < 5 μg kg–1) for most of the target pesticides. The method was applied to the determination of pesticides at low μg kg–1 in tomato, cucumber, green soybeans, spinach, grapes, and green tea.
Recent advances in the isolation and structural studies of biomacromolecules using microcolumn techniques
Authors: Novotny Milos 
Published: May 2005

AbstractMicrocolumn liquid chromatography and capillary electrophoresis facilitate isolation of biological macromolecules at subnanogram levels. In order to characterize structurally such small amounts of labile materials, it is essential to develop new nanoscale sample treatment approaches and highly sensitive analytical techniques for the determination of biomolecular fragments. Progress in this area is summarized, using selected examples of the amino acid, peptide, and oligonucleotide separations.
Flow rate control in pressure‐programmed capillary supercritical fluid chromatography
Authors: Janssen Hans‐Gerd , Rijks Jacques A. , Cramers Carl A. 
Published: May 2005

AbstractA versatile and simple system is described that allows variation of the column flow rate in open‐tubular capillary supercritical fluid chromatography using both on‐column and postcolumn detection. The system is based on column‐effluent splitting in a low‐dead‐volume T piece at the column exit just before detection. The flow is split into two streams. One stream is fed to a flame ionization detector, and the second is used to control the overall mass flow through the column. Flow through linear restrictors is studied as a function of the pressure drop over the restrictor at ambient temperature. We derived a simple relationship from this study that quantifies the flow rate characteristics of the dual‐restrictor system as a function of the column pressure and the restrictor back pressure.The variable‐flow system was employed to control independently column pressure and mass flow rate in pressure‐programmed analysis. Resolution in flow‐controlled pressure‐programmed elution was shown to be superior to that achieved in fixed‐restrictor systems. Furthermore, the applicability of the system as a convenient means of measuring Van Deemter curves and diffusion coefficients is demonstrated.
Large‐volume sample introduction into narrow‐bore gas chromatography columns using thermal desorption modulation and signal averaging
Authors: Liu Zaiyou , Phillips John B. 
Published: May 2005

AbstractA small diameter (50 μm) open‐tubular gas chromatographic column can be made to accept relatively large volume samples. A conventional injection port and a short length of a 530‐μm‐diameter column are used to accept and hold the sample while it is fed slowly into the 50‐μm column. An injection of such large volume and slow speed normally is quite incompatible with this small, fast column. An on‐column thermal desorption modulator at the head of the column matches the sample to the column by chopping the injected sample into many fast concentration pulses. Signal averaging of the resulting fast chromatograms gives a total sample chromatogram. The method is adaptable to either gaseous or liquid samples.
Current aspects of stationary phase immobilization in open tubular column chromatography
Authors: Blomberg Lars G. 
Published: May 2005

AbstractIn situ stationary phase immobilization in principle can be attempted in two different ways: using thermal methods or radical‐initiated reactions. Thermal immobilization, in general, is applied for the preparation of columns to be used at ultra‐high temperatures, and radical‐initiated immobilization can be applied in most other cases. For polar, narrow‐bore, and thick‐film columns, low immobilization temperatures are preferred. The reactions involved in the different immobilization methods are described in this review, and the advantages and disadvantages of current immobilization methods are discussed.
A step gradient system for microcolumn liquid chromatography based on a multiple‐loop valve
Authors: Banks J. Fred , Novotny Milos V. 
Published: May 2005

AbstractA new gradient elution system for microcolumn liquid chromatography is presented and evaluated. A multiple‐loop valve system facilitates a reproducible, stepwise addition of the mobile phase at low‐microliter‐per‐minute flow rates. The system is amenable to automation. Gradient precision has been evaluated under various operational conditions. An optimized system yielded standard deviations in retention times of less than 0.5 on runs over 2 h.
Efficiency of packed microcolumns compared with large‐bore packed columns in size‐exclusion chromatography
Authors: Kennedy Robert T. , Jorgenson James W. 
Published: May 2005

AbstractColumns with inner diameters of 50 and 28 μm were slurry‐packed with 4–5 μm size‐exclusion chromatography particles (Du Pont GF 250 Zorbax Bioseries) and compared with a commercially prepared 9.4‐mm i.d. column that was packed with the same particles. The columns were compared on the basis of efficiencies, peak shapes, and van Deemter coefficients obtained for three proteins used as test analytes. The microcolumns provided more symmetrical peak shapes and lower plate heights than those provided by the commercial column if the peaks were analyzed using statistical moments. For example, hmin for bovine serum albumin was 5.6 in the commercial column and 2.1 in the microcolumn. This difference is attributed to the quality of the packing process, based on the fact that the van Deemter A term was significantly lower for the microcolumn than for the conventional column. The van Deemter data demonstrate that the A term was the major source of band broadening in the commercial column throughout the range of velocities used, and both the A and C terms were significant for the microcolumn. A 90 cm × 50 μm column was prepared and showed approximately 80% of the expected increase in efficiency.
Capillary zone electrophoresis of dilute samples with isotachophoretic preconcentration
Authors: Dolnik Vladislav , Cobb Kelly A. , Novotny Milos 
Published: May 2005

AbstractA method for concentrating dilute samples prior to separation by capillary zone electrophoresis (CZE) is described. The principles of isotachophoresis are used to achieve higher local concentrations of the sample solution within a preconcentration capillary that is attached directly to the CZE separation capillary. Through a judicious choice of leading, terminating, and background electrolytes, the isotachophoretic preconcentration step can be performed on‐line with the CZE separation using common CZE instrumentation. The use of isotachophoretic preconcentration allows larger volumes of dilute sample solutions to be analyzed effectively in the zone electrophoretic mode, thereby reducing the stringent CZE requirements of small sample volumes and concentrated sample solutions.
Capillary electrophoresis applied to the analysis of pharmaceutical compounds
Authors: Wainright Ann 
Published: May 2005

AbstractSeparations by capillary zone electrophoresis (CZE) in plain, uncoated fused silica capillaries were compared with those in electroendosmosis‐free coated capillaries. For small ions, exemplified by some anti‐inflammatory drugs, resolution and analysis times were comparable in the two types of capillaries. The advantage of the coated capillary was that it predictably eluted all negative analytes regardless of electrolyte pH. The uncoated capillary, on the other hand, allowed separation of both positive and negative species in one run, provided that the electroendosmotic flow was sufficiently high to elute all negatively charged analytes. Because electrolyte conditions were established that eluted all sample analytes, subsequent analyses were performed in uncoated capillaries.Antibiotics such as sulfonamides, cephalosporins, and penicillins were separated by zone electrophoresis. Optimal separation conditions were established by varying the pH and ionic strength of the electrolyte. For the separation of structurally similar peptides and barbiturates, micellar electrokinetic capillary chromatography (MECC) was the method of choice because the structural differences conferred differences in hydrophobicity.The feasibility of using CZE in pharmaceutical analysis was shown in the evaluation of over‐the‐counter pain, cold, and allergy medications. These typically gave relative standard deviations of 1% for retention times and 3% for peak areas.
Effects of buffer composition on electroosmotic flow in capillary electrophoresis
Authors: VanOrman Barbara B. , Liversidge Gary G. , McIntire Gregory L. , Olefirowicz Teresa M. , Ewing Andrew G. 
Published: May 2005

AbstractSolute migration in capillary electrophoresis is the sum of the molecularly specific electrophoretic mobility and the electric‐field‐induced solvent flow (electroosmosis). This solvent flow is an important component of capillary electrophoresis and has been linked to resolution and automation aspects of this technique. This work demonstrates that equivalent electroosmotic flows can be achieved using different buffer types if the ionic strength is equal in the two systems. The effects of the addition of acetonitrile and several different alcohols on electroosmotic flow are also examined. The data suggest a unique surface effect of alcohols on the observed electroosmotic flow.
Electron spin resonance studies of inorganic radicals
Authors: Symons Martyn C. R. 
Published: May 2005

AbstractA brief review is given of the ways in which ESR spectroscopy has been used to shed light on the electronic structures of simple inorganic radicals. These include atoms (H·, N, O2·, Ag·); diatomic radicals (·OH, ·NO, O), AB2 species(·CO2−, ·NO2, HĊO, O, etc.), AB3 species (·NH3+, ·CH3, ·BH3−, ·NO, ·SO3−, NO3·, H2ĊN, etc.) and AB4 centres (PO, ·PO, ·PF4, etc.). Matrix effects on these species are described and rationalized, and aspects of reaction mechanisms in which they participate are discussed.
EPR study of iron—nitrosyl clusters in the oxidation of Fe(NO)2(CO)2
Authors: Li Lijuan , Morton John R. , Preston Keith F. 
Published: May 2005

AbstractThe oxidation of Fe(NO)2(CO)2 by tetracyanoethylene (TCNE), by the nitrosonium ion (NO+), or by electrolysis in polar solvents was studied by EPR spectroscopy. A number of long‐lived (τ1/2 of the order of hours) free radicals were detected in the early stages of reaction, all having similar isotropic g‐factors and 14,15N hyperfine interactions. These have been identified as the mononuclear cations, Fe(NO)2(CO)2−nStn+ (St = solvent molecule). They slowly disappear and are replaced by persistent radicals (τ1/2 of the order of days) that show equal isotropic hyperfine interactions with four‐, six‐ or eight‐nitrogen nuclei. Infrared and EPR spectroscopic data suggest that two of these species are trinuclear nitrosyl clusters, Fe3(NO)2n(CO) (n = 3, 4), in which the unpaired spin is localized on one iron nucleus, but which are fluxional on the EPR time‐scale. The third nitrosyl radical with four equivalent NO ligands is tentatively identified as a binuclear intermediate that may be a precursor of the trinuclear clusters.
Review of recent EPR and theoretical studies on the addition of free radicals to C60 and C70
Authors: Morton John R. , Negri Fabrizia , Preston Keith F. 
Published: May 2005

AbstractEPR spectra of free‐radical adducts of C60 and C70 are described and discussed. In the case of addition to C60 the prototype radical is HC60 or perhaps MuC60. The H/Mu hyperfine anomaly in these radicals is explained. The spectra of alkyl‐C60 and fluoroalkyl‐C60 radicals are also described, including factors determining the equilibrium configuration over the C60 surface of radicals of the general formula XYZCC60. The structure of the higher adducts R3C60 and R5C60 is mentioned. In the case of H addition to C70, four of the five possible isomers of HC70 have been identified, but only one of the 2792 isomers of H3C70 is reported.
Simultaneous ESR measurements of the kinetics of oxygen consumption and spin label reduction by mammalian cells
Authors: Morse Philip D. , Smirnov Alex I. 
Published: May 2005

AbstractNitroxide spin labels and probes were applied to measurements of cell redox activities and oxygen concentration by ESR. Current experimental methods often require large numbers of cells and monitoring of only the amplitude of the ESR signal. This can result in experimental artifacts and data misinterpretation. An improved method is described for accurate measurement of nitroxide intensity and linewidth, which in turn provides information about cell redox activities and oxygen concentration. The method is based on fitting of ESR spectra using a fast convolution least‐squares algorithm suitable for inhomogeneously broadened ESR lines. All fitting parameters, including the Lorentzian component of the linewidth and the double integrated intensity, are extracted from the experimental spectra directly. The experiments were carried out at cell concentrations of 5 × 106 cell ml−1 or less to prevent cell crowding and at initial nitroxide concentration of 1 mM or 100 μM to ensure that nitroxide metabolism by the cells was not diffusion limited. Examples include experiments with cultured baby hamster kidney and adenovirus transformed hamster cells using the nitroxide radicals TEMPOL (2,2,6,6‐tetramethylpiperidine‐N‐oxyl‐4‐ol) and 15N‐labeled perdeuteriated TEMPONE (15NPDT) (2,2,6,6‐tetramethylpiperidine‐N‐oxyl‐4‐one). Under these experimental conditions, the rates of nitroxide metabolism derived from changes in nitroxide intensity are independent of oxygen concentration.
Temperature and orientation dependence of electron spin relaxation in molybdenum(V) porphyrins
Authors: Husted Rebecca , Du Jing‐Long , Eaton Gareth R. , Eaton Sandra S. 
Published: May 2005

AbstractElectron spin lattice relaxation rates were measured by saturation recovery for three oxo(5,10,15,20‐tetratolylporphyrinato)molybdenum(V) complexes, OMo(TTP)X, X=Cl−, OH−, OEt−. For O=Mo(TTP)(OEt) in glassy solution between 15 and 130 K the temperature dependence of 1/T1 is consistent with a two‐photon Raman process. For each of the complexes at 100 K 1/T1 is faster when the magnetic field is in the molecular plane than when it is perpendicular to the molecular plane, which is attributed to orientation dependence of intramolecular vibrations. The orientation‐dependent values of 1/T1 are approximately the same for isotopes with I = 0 or I = 5/2, which indicates that molybdenum nuclear hyperfine interaction is not a major factor in the electron spin‐lattice relaxation rate. Phase memory relaxation rates were measured by electron spin echo. Below about 90 K 1/Tm is weakly temperature dependent and becomes more strongly temperature dependent at higher temperature as 1/T1 approaches 1/Tm and as the host lattice softens. For isotopes with I = 5/2 at 100 K 1/Tm is faster at molecular orientations for which the resonant field is more strongly dependent on small changes in molecular orientation.
Atom positions from hyperfine data for germanium centers in α‐quartz
Authors: Mombourquette M. J. , McEachern R. J. , Weil J. A. 
Published: May 2005

AbstractGermanium 3+ occurs in α‐quartz substitutionally for silicon 4+, either as complex anions [GeO4]− or these anions charge‐compensated with interstitial alkali cations, i.e. as two primary types of species denoted by [GeO4/M], where M = Li, Na. A brief review of the relevant literature is presented. Using the molecular‐orbital spin population for the unpaired electron in each center, available from 73Ge and 17O hyperfine data, an evaluation of the likely M+ positions within the quartz structure has been performed. In part, the present calculations were done to test the well known McConnell‐Strathdee approach with well defined experimental hyperfine data. A generalized discussion of atom‐position determination by EPR, and problems encountered in the process, is included.
Radical cations of precursor compounds for organic conductors derived from carbohydrates: An ESR study
Authors: Scholz Markus , Gescheidt Georg , Schöberl Ulrich , Daub Jörg 
Published: May 2005

AbstractThe radical cations of two electron donors containing two 1,3‐dithiol moieties were characterized by the use of ESR/ENDOR/general TRIPLE spectroscopy. The spin population resides mainly in the central part of the molecules. The g‐factors are correlated with the 33S coupling constants, which are determined from satellite lines.
ESR measurement of translational diffusion constants
Authors: Fawthrop Susan A. , Gillies Duncan G. , Sutcliffe Leslie H. , Symms Mark R. 
Published: May 2005

AbstractESR spectroscopy can be used to measure the translational diffusion constants of spin probes in a variety of media using a capillary method. Following preliminary work, it has been possible to improve upon the accuracy of determining diffusion constants in two ways. Both methods require an experimental measurement of the resonant cavity sampling profile. In the first procedure, this cavity profile is convolved with a trial Gaussian distribution and the result is compared with the experimental data obtained from the ESR measurements; the diffusion constant is then determined by graphical optimization. The second method is a graphical one based on a knowledge of the experimental diffusion profile and the cavity sampling profile. Both methods have been shown to give similar results but the second less rigorous corrected‐zero method is generally simpler to apply. For a medium such as water, it takes several days to acquire the necessary experimental data but the time taken to carry out the experiment can be shortened (or slower rates of diffusion can be measured) by using a shielded resonant cavity.
Synthesis and ESR of a nitroxide biradical of approximate D2h symmetry
Authors: Fabre Claude , Gambarelli Serge , Jaouen Daniel , Rassat André , Brunel Louis‐Claude , Chachaty Claude 
Published: May 2005

AbstractA nitroxide biradical 2,6‐dioxy‐2,6‐diaza‐1,1,3,3,5,5,7,7‐octamethyldicyclopentano[b;e]pyridine (1) and the corresponding monoradical (2‐oxy‐6‐hydroxy) were prepared starting from 2,2,5,5‐tetramethyl‐3‐oxopyrrolidine by successive condensation with formaldehyde (KOH) or DMF (K in THF), NH4OAc and oxidation (Na2WO4‐H2O2). In ethanol, biradical 1 shows a quintet (|J| ≫ |aN| = 14.6 G). In frozen ethanol solution, the experimental spectra (X‐band at 120 K and 240 GHz at 7, 15 and 25 K) can be computer simulated with the following parameters: D = −64 G; E = 1 G; gxx = 2.0093; gyy = 2.0064; gzz = 2.0020; Axx = Ayy = 8 G; Azz = 32.2 G. From the temperature dependence of the high‐field spectra, D is found to be negative.