bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reproducibility in capillary supercritical fluid chromatography: Comparison of injection techniques
Authors: Richter B. E. , Knowles D. E. , Andersen M. R. , Porter N. L. , Campbell E. R. , Later D. W. 
Published: May 2005

AbstractAn analysis of the precision obtained using commercially available microvalve injectors is reported for three modes of injection: conventional split; timed‐split; and direct. Results from this study show that good precision (< 3% RSD for external standard and < 1% RSD for internal standard methods) can be obtained with capillary supercritical fluid chromatography (SFC). However, particular attention must be paid to the type of valve used, the orientation of the column relative to the valve, the mode of interfacing or connecting the column to the valve, and the type of pressure or density programming used for the analysis as all of these factors will affect the reproducibility.
Capillary and packed column SFC/MS
Authors: Berry A. J. , Games D. E. , Mylchreest I. C. , Perkins J. R. , Pleasance S. 
Published: May 2005

AbstractA frit restrictor interface for capillary column supercritical fluid chromatography/mass spectrometry (SFC/MS) has been constructed and used for the analysis of high boiling point alkanes. Packed column SFC/MS is described using both a moving belt liquid chromatographic/mass spectrometric interface and a thermospray source in the filament‐on mode.
Use of small diameter WCOT columns for ultra‐high resolution GC/MS
Authors: Hyver K. J. 
Published: May 2005

AbstractFor clinical and environmental analyses utilizing capillary gas chromatography/mass spectrometry (GC/MS), increased sensitivity and speed of analysis are highly desirable. These performance advantages are realized using a WCOT column of 100 μm i.d. as compared to the more conventional 200 μm i.d. capillary columns. The improved sensitivity of capillary direct GC/MS with the 100 μm i.d. column for the confirmation of drugs of abuse will be demonstrated. For environmental analysis, the superior efficiency and resolution of the 100 μm i.d. column can be employed for the separation of priority pollutants. This approach is more amenable to capillary direct GC/MS providing a more effective interface to the mass spectrometer. As a result improved sensitivity and a considerable decrease in analysis time is achieved over that obtained with the larger diameter environmental specialty phase columns.
Determination of soil fumigants in air using tandem capillary gas chromatography after charcoal trapping
Authors: Tuinstra L. G. M. Th. , Traag W. A. , Roos A. H. 
Published: May 2005

AbstractSoil fumigants, like 1,3‐dichloropropene and metham‐sodium (forming methyl isothiocyanate) diffuse into the atmosphere, thus presenting a hazard to people in the surroundings. A method is described in which a large volume (50 μl) of extractant, used to desorb the compounds from charcoal, is injected into a GC, equipped with two capillary columns. By way of Deans switching, the solvent is separated from the compounds of interest. Modification of a GC sampler makes unattended analyses possible.
Computer‐controlled vacuum backflush for capillary GC
Authors: Rankin Christine , Sacks Richard 
Published: May 2005

AbstractA vacuum‐pump‐operated backflush system has been developed for applications involving high‐speed, repetitive GC analysis of gas streams containing ppm and ppb levels of organic vapor. The system uses an injector capable of cryofocusing and a relatively short length of 0.25‐mm i.d. fused silica column for the separation of relatively simple mixtures of volatile compounds. Analysis times typically are in the 5–10 s range, and backflush times are in the 2–5 s range. Gases from the flame ionization detector are used as the backflush carrier gas, and no modification of the detector is necessary. A procedure is described which allows the average gas velocity to be measured during backflush operation. The minimum backflush time is directly proportional to the analysis time and to the square of the column length, making this system most useful with short columns and short analysis times.
On‐line solvent evaporator for coupled LC systems
Authors: Grob Konrad , Tönz Barbara 
Published: May 2005

AbstractThe mobile phase of a fraction eluted from a first LC column is removed by an on‐line evaporator in order to reconcentrate the solute material or to exchange the eluent before performing a subsequent LC separation. Evaporation essentially occurs by concurrent evaporation, i.e. the solvent evaporates at a rate equal to the flow rate of the incoming eluent, and is driven by the overflow principle, i.e. vapors leave the tube as a result of the expansion resulting from evaporation.The liquid is introduced into a small tube (e.g., 4 cm × 1.3 mm i.d.) which is packed, e.g., with a coarse silica gel. The outlet of the evaporator is connected to vacuum in order to enable evaporation at reduced temperature and to increase retention of the volatile components. With normal phase eluents, evaporation rates may approach 1 ml/min; n‐dodecane was the most volatile n‐alkane fully retained by the evaporator.
Improved method for the determination of sulfur components in natural gas
Authors: Tuan Hai Pham , Janssen Hans‐Gerd , Kuiper‐van Loo Ellen M. , Vlap Harm 
Published: May 2005

AbstractDetermination of trace concentrations of sulfur components in natural gas is a true analytical challenge. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. In the present contribution the sample pretreatment and chromatographic separation steps have been evaluated and optimized based on the use of a flamebased sulfur chemiluminescence detector (SCD) for target compound detection.The proposed instrument consists of a programmed temperature vaporizing (PTV) injector employing a liner packed with Chromosorb 104, a 4 μm thick film apolar column and a flame‐based SCD. Using a 13 mL sample loop the detection limit achievable with the new method is 3 μg S/m3. The precision of replicate measure. ments is generally in the range of 5–15% relative standard deviation. Lower detection limits can be achieved by preconcentrating larger sample volumes, e.g. 100 mL.
Optimization of selectivity in capillary zone electrophoresis and micellar electrokinetic capillary chromatography using the iterative regression strategy
Authors: Corstjens Hugo , Oord André E. E. , Billiet Hugo A. H. , Frank Johannes , Luyben Karel Ch. A. M. 
Published: May 2005

AbstractAn iterative regression design has been used in the optimization of selectivity in capillary zone electrophoresis and micellar electrokinetic capillary chromatography. This strategy, initially developed for HPLC, is modified in respect of the choice of the parameter(s) and the parameter space and the description of the migration behavior of (charged) solutes in capillary electrophoresis. The six test solutes could not be fully resolved by adjusting the pH in a free zone system but the simultaneous two‐parameter optimization of the pH and the concentration of surfactant resulted in baseline separation of all the solutes. Further improvement may be obtained when distorted peak shapes are also considered at the level of the parameter choice and the criterion.
Microextraction by demixing of two miscible solvents for the determination of phenols in water
Authors: Onuska Francis I. , Terry K. A. 
Published: May 2005

AbstractA method for the determination of anionic solutes such as phenol, cresols, and xylenols present in industrial effluents has been developed. It is based on microextraction using two miscible phases followed by demixing of the phases by the addition of ammonium sulfate. The extraction properties of 2‐propanol were examined and the procedures were optimized. High resolution gas chromatography–mass spectrometry in the selected ion monitoring mode was used as a separation and quantitation technique. This method is rapid and precise and allows detection limits of 1 μg L−1 to be easily obtainable employing a 50 mL water sample.
Correlation between structure of dihydropyridine calcium antagonists and their retention behavior and enantioseparation on the β‐cyclodextrin stationary phase in HPLC
Authors: Tesarová E. , Gilar M. , Hobza P. , Kabelác M. , Deyl Z. , Smolková‐Keulemansová E. 
Published: May 2005

AbstractChromatographic data for five dihydropyridine calcium antagonists (CAs) were obtained on β‐cyclodextrin column in the reversed phase HPLC. Interaction energies of solute‐cyclodextrin complexes formed by docking of different parts of the CAs' molecules into the cyclodextrin cavity were calculated. Results from the HPLC experiments and molecular modeling were compared. It was found that several types of inclusion complexes are energetically possible and contribute to the retention simultaneously. Only certain inclusion complex are assumed to be responsible for enantioseparation of CAs. Nevertheless molecular modeling studies are a useful tool for explaining the enantioselectivity and predicting the elution order of enantiomers.
Molecular recognition and self‐replication
Authors: Rebek Julius 
Published: May 2005

AbstractSelf‐replicating molecules stand at the very boundary of chemistry with biology. This review describes the development of synthetic structures capable of self‐replication from studies in molecular recognition. The weak intermolecular forces—hydrogen bonds and aromatic stacking interactions—that characterize interactions of nucleic acid components were designed into synthetic receptors for adenine. Covalent conjugates of these receptors with adenines gave self‐complementary structures capable of replication. The new systems feature autocatalysis, sigmoidal product growth and even mutation. General rules for the design of replicating systems are described and these suggest that the evolution of replicating molecules was an inevitable event.
Intermolecular interactions in type I collagens
Authors: David Carl W. 
Published: May 2005

AbstractX‐PLOR modelling of collagen dimers containing Gly‐Glu‐Arg in each chain has been carried out. The interaction between molecules when two Gly_Glu‐Arg are present on each chain is found to be substantially less than two times that obtained with one per chain, implying that relative tilting of two collagen molecules does not offset the disadvantages of misalignment of the interacting moieties. This implies that if multiple (Glu−‐Arg+)3 interactions are important in fibril formation, their lateral separations must be large enough to insure that they act independently.
Vibrational spectra of substituted platinum(IV) ammine complexes. I: [Pt (NH3)6]4+; [Pt (NH3)5X]3+, X = Cl, Br; mer [Pt (NH3)3Cl3]+and [Pt(NH3)Cl5]−
Authors: Nolan M. J. , James David W. 
Published: May 2005

AbstractThe Raman and infrared spectra (4000–40 cm−1) have been recorded for the salts [Pt (NH3)6]Cl4, [Pt (NH3)5X]X3 (X = Cl, Br), mer [Pt (NH3)3Cl3]Cl and K [Pt (NH3)Cl5], in the solid state. The results are primarily explicable on a point group model for the complex ion. For the monohalo and pentahalo derivatives solution Raman spectra were recorded. These indicated that solid state effects are more pronounced for the monohalo derivatives.
Vibrational spectra of substituted platinum(IV) ammine complexes. II: cis and trans isomers of [Pt (NH3)4X2]2+and [Pt (NH3)2x4] where X = Cl, Br and I
Authors: James David W. , Nolan M. J. 
Published: May 2005

AbstractThe Raman and infrared spectra (4000–40 cm−1) have been obtained for many compounds of the series [Pt(NH3)4X2]2+ and [Pt (NH3)2X4] (cis and trans isomers) where X = Cl, Br, I. The spectra have been interpreted using the point‐group and factor‐group approaches.
Raman spectra and phase transition of ammonium paraperiodate (NH4)2 H3IO6
Authors: Poulet H. , Mathieu J. P. 
Published: May 2005

AbstractPolarized Raman spectra of single crystals of (NH4)2IO6 are recorded at 270 K and 24 K and analyzed. The failure of the selection rules does not allow a choice between the two structures proposed for the low temperature phase.
Raman spectra and crystal structures of methyl halides
Authors: Takeuchi H. , Bribes J.‐L. , Harada I. , Shimanouchi T. 
Published: May 2005

AbstractThe Raman spectra of crystalline methyl halides and the deuterated analogues were investigated at liquid nitrogen temperature. The weak band newly observed at 156 cm−1 in the spectrum of CH3Cl has been assigned to the rotational lattice mode about the molecular symmetry axis. Three translational lattice vibrations were also found at 84, 71, and 60 cm−1 for CH3Cl (83, 68, and 59 cm−1 for CD3Cl). Of the seven and six lattice vibrations of methyl bromide and methyl iodide, respectively, two higher frequency bands were assigned to the rotational modes and the rest were assigned to the translational modes. The present experimental results are interpreted in terms of the crystal structures, C2ν for methyl chloride and D2h for methyl bromide and methyl iodide.
A Raman spectroscopic investigation of the conformation of the cyclohexyl halides C6H11X (X = Cl, Br and I) in thiourea clathrates
Authors: Allen A. , Fawcett V. , Long D. A. 
Published: May 2005

AbstractThe Raman spectra of the cyclohexyl halide‐thiourea clathrates have been investigated. It is found that whereas cyclohexyl chloride and bromide exist only in the axial conformation in the clathrate, cyclohexyl iodide exists in both the axial and equatorial conformations in the clathrate.
Raman and IR spectra of matrix isolated OsO3F2 AND OsO4: The molecular shape of monomeric OsO3F2
Authors: Beattle I. R. , Blayden H. E. , Crocombe R. A. , Jones P. J. , Ogden J. S. 
Published: May 2005

AbstractThis paper reports fundamental vibration frequencies for molecular OsO3F2 and OsO4 isolated in argon matrices at low temperatures. OsO3F2 is shown to have D3h symmetry on the basis of Raman and IR selection rules, and this conclusion is confirmed by the results of 18O enrichment studies which demonstrate the presence of an OsO3 unit containing three equivalent oxygens. The argon matrix frequencies are 946.5 (A′1), 928.5 (E′), 646 (A′2), 619 (A′/1) 348 (E″), 316.5 (E′) 258 (A″2) and 206 (E′) cm−1. High resolution spectra are also reported for matrix isolated Os16O4 (ν1 963, ν2 332, ν3 956, and ν4 327 cm−1) and for 18O enriched OsO4 species.
Liaison hydrogène en phase liquide et spectrométrie Raman. IV—structure des polymères du méthanol liquide pur et dissous en solvants inertes
Authors: Maillard D. , Perchard C. , Perchard J. P. 
Published: May 2005

AbstractCalculations of νOH vibrational frequencies and of the corresponding IR and Raman intensities have been carried out according to two models of polymerization of alcohols (chains and cycles). They are compared to experimental spectra of methanol (pure liquid and solutions in CCl4) and of isopropanol dissolved in freons at low temperature. For methanol at 295 K, the best fit is obtained for a cyclic structure of polymers, with an average degree of polymerization of 5–6; for isopropanol at 106 K cyclic tetramers are preponderant.
Polarized Raman spectra and intermolecular potential of DL‐alanine crystal
Authors: Machida Katsunosuke , Kagayama Akira , Saito Yutaka 
Published: May 2005

AbstractPolarized Raman spectra of DL‐alanine and N‐deuterated DL‐alanine single crystals have been recorded. A normal coordinate analysis has been made for the optical active intra‐ and intermolecular vibrations of DL‐alanine crystal. As in the case of L‐alanine crystal, large factor group splittings were observed for the CH3 asymmetric deformation mode. The magnitudes of the observed splittings are elucidated well by the empirical potential function of the exp‐6 type for the non‐bonded atom‐atom interaction. The differences in the NH3 rocking and the CH3 rocking frequencies between L‐ and DL‐alanine crystals are ascribed to the differences in the intermolecular potential and the molecular geometry, respectively. A good agreement was obtained between the observed and the calculated lattice frequencies.
Raman investigation of palladium oxide, rhodium sesquioxide and palladium rhodium dioxide
Authors: Weber W. H. , Baird R. J. , Graham G. W. 
Published: May 2005

AbstractRaman spectra were obtained from PdO, Rh2O3 and PdRhO2 thin films formed by oxidizing foil samples. Polarization measurements allow symmetry species assignments to be made for the lines from the corundum phase of Rh2O3 and from PdRhO2, which has a delafossite structure.
Perturbation theoretical study of resonance Raman intensities: Contribution of forbidden electronic states
Authors: Okamoto Hiromi 
Published: May 2005

AbstractAn equation which describes vibrational resonance Raman intensities was derived using the non‐adiabatically expanded (to the second order) state vector and the damped Kramers‐Heisenberg‐Dirac dispersion equation. The equation obtained includes the terms which correspond to the equation previously proposed by Albrecht, by Zgierski and by Korenowski et al. Forbidden electronic states may contribute to Raman intensities through the second‐order terms. The Raman excitation profile is predicted to show a characteristic pattern for a system where one of these second‐order terms plays an important role. The physical meanings of these higher order terms are discussed.
Surface‐enhanced Raman scattering of nucleic acid components in silver sol: Uracil and its derivatives
Authors: Oh Weon Sik , Suh Se Won , Kim Myung Soo 
Published: May 2005

AbstractThe surface‐enhanced Raman scattering (SERS) of uracil, uridine, 2′‐deoxyuridine and 5′‐rUMP adsorbed on aqueous silver sol was investigated. Uracil was found to adsorb as the N‐3 deprotonated form, which underwent a reorientation from the situation where the base was perpendicular to the surface to the situation where the base lay flat on the surface as the surface charge was made more negative. The N‐3 deprotonated molecules of uridine, 2′‐deoxyuridine and 5′‐rUMP were found to lie flat on the silver surface regardless of the bulk concentration and the silver surface charge.
Vibrational dephasing in liquid germane
Authors: Wilde Richard E. 
Published: May 2005

AbstractRaman spectra are reported for the n̈1 bands of germane and germane‐d3. Fourier transformation of the band shapes provided vibrational autocorrelation functions. These functions were modeled by a memory‐function procedure. Evidence for resonant vibrational energy transfer and higher order cumulant‐expansion terms was found in an isotopic‐dilution study.
Raman study of the effect of LiCl and CsCl on the resonance intermolecular coupling and the Fermi resonance of water
Authors: Sokołowska Anna 
Published: May 2005

AbstractChanges in the isotropic and anisotropic component contours of the H2O and D2 stretching bands in aqueous solutions of LiCl and CsCl were studied within the entire accessible concentration range. The isotropic component contours were resolved into three constituents and the anisotropic contours into four. The resonance intermolecular coupling constants, V1 for the ν1 vibration and V2 for the 2ν2 overtone, and the Fermi resonance constant, W, of water were determined for solutions of various electrolyte concentrations. The added electrolytes were found to lower the V1 and V2 values. The Fermi resonance coupling constant decreased in aqueous LiCl solutions and was constant in CsCl solutions. The unperturbed ν1 and 2ν2 band positions of the LiCl solutions did not change. In the CsCl solutions, ν1 shifted to lower frequencies and 2ν2 to higher frequencies. A new component was found to appear in the anisotropic component for concentrated LiCl solutions, at 3550 cm−1 for H2O and 2590 cm−1 for D2O.
Raman–Rayleigh scattering measurements in reacting and non‐reacting dilute two‐phase flows
Authors: Masri A. R. , Dibble R. W. , Barlow R. S. 
Published: May 2005

AbstractSimultaneous space‐ and time‐resolved measurements of scalars were made in reacting and non‐reacting dilute, two‐phase, jet flows of methanol. The spontaneous Raman–Rayleigh scattering technique was used to measure temperature and the concentrations of CH3OH, O2, N2, H2, H2O, CO and CO2. In the reacting case, laserinduced fluorescence from the hydroxyl radical was jointly measured. The two‐phase flow is formed at atmospheric pressure at the exit of an axisymmetric jet centered in a co‐flowing stream of air. At the measurement location of ten fuel jet diameters downstream of the nozzle exit plane the volume percentage of liquid in the center of the jet is estimated at about 0.015%. The Rayleigh‐scattered signal can only be used as a marker for the existence of liquid in the measurement volume as it is overhwlemed by Mie and possibly geometrical scattering from droplets. The methanol Raman signal from the liquid–gas mixture increases, mainly owing to the increase in the number density of molecules and the local field effect. Raman signals from other gaseous species are not affected by the existence of droplets in the measurement volume. Gas‐phase temperature is obtained from the sum of the species number densities. The fluorescence from OH shows occasional unrealistic overshoots for rich mixtures, which indicates some interference due to the existence of droplets.
The quaternary structure of Alfalfa mosaic virus
Authors: Mellema Jan E. , van Den Berg Hans J. N. 
Published: May 2005

AbstractFrom an analysis of electron micrographs of Alfalfa Mosaic Virus (AMV), evidence has been obtained which favors a cylindrical P6 lattice for the protein coat of the virus. For the analysis use was made of optical diffraction and computer processing of electron images of negatively stained virus particles.The virus coat exhibits polymorphism. Two kinds of structure were found: a stacked and a helical type. In the stacked type of lattice the unit cells are arranged in staggered rings in such a way that two rings comprise a repeat distance of the structure. The selection rule for the optical diffraction patterns of the stacked form is 1 = n + 2m, in which n is an integer multiple of 3. The layerlines are equally spaced at a distance of approximately 1/80 Å−1.In the helical type of lattice these rings of unit cells are transformed into turns of a double helix. The selection rule derived in this case is 1 = 6n − 17m, in which n is an integer multiple of 2. The repeat of the structure is approximately 440 Å.
Effects of sodium ions on the electrical and pH gradients across the membrane of streptococcus lactis cells
Authors: Barker Susan L. , Kashket Eva R. 
Published: May 2005

AbstractEnergized cells of Streptococcus lactis conserve and transduce energy at the plasma membrane in the form of an electrochemical gradient of hydrogen ions (Δp). An increase in energy‐consuming processes, such as cation transport, would be expected to result in a change in the steady state Δp. We determined the electrical gradient (ΔΨ) from the fluorescence of a membrane potential‐sensitive cyanine dye, and the chemical H+gradient (ΔpH) from the distribution of a weak acid. In glycolyzing cells incubated at pH 5 the addition of NaCl to 200 mM partially dissipated the Δp by decreasing ΔΨ, while the ΔpH was constant. The Δp was also determined independently from the accumulation levels of thiomethyl‐β‐galactoside. The Δp values decreased in cell fermenting glucose at pH 5 or pH 7 when NaCl was added, while the ΔpH values were unaffected; cells fermenting arginine at pH 7 showed similar effects. Thus, these nongrowing cells cannot fully compensate for the energy demand of cation transport.