bluuebunny/crossref_metadata_2025_split huggingface dataset:
Capillary electrokinetic separations: Influence of mobile phase composition on performance
Authors: Sepaniak Michael J. , Swaile David F. , Powell A. Craig , Cole Roderic O. 
Published: May 2005

AbstractThe composition of the mobile phase employed in capillary zone electrophoresis and the related technique, micellar electrokinetic capillary chromatography, is an important factor in determining separation performance. The influences of ionic salt, surfactant, and organic solvent mobile phase additives on separation efficiency, retention, and elution range are discussed and demonstrated.
Band broadening effects in capillary column recycle gas chromatography with valves
Authors: Zhang Q. W. , Hathcock L. , Bertsch W. 
Published: May 2005

AbstractSources leading to band broadening and peak distortion have been studied in a capillary column recycle system, based on a commercial microvalve. The ferrule system was a major contributor to band broadening. It was found that the quality of connections is very critical but the internal volume of the valve is not important. The pressure pulses resulting from each switching operation produced some band broadening with substances that had just been transferred through the valve but no adverse effects were noticed when they had travelled some distance into the column. Flow into valve cavities and through tees also produced a drop in efficiency. It is not clear whether this is solely due to problems in column connection or if changes in flow pattern also contribute.The activity of the valve toward polar substances was also assessed. No attempt was made to deactivate valve surfaces. The components of the Grob test mixture were almost unaffected but highly polar and acidic compounds such as nitrophenol showed severe losses. No evidence for catalysis was found.
Influence of extra‐column effects in capillary gas chromatography
Authors: Bemgård Agneta K. , Colmsjö Anders L. 
Published: May 2005

AbstractThe contribution of extra‐column effects to the height equivalent to a theoretical plate (HETP) in capillary gas chromatography is calculated. Four extra terms are added to the Golay‐Giddings equation and evaluated in order to verify their significance. The paradox of negative A terms is resolved by curve fitting of experimental values to the theoretical function of HETP, including the extra‐column effects. The importance of the A term and the diffusion process for an injection in split mode were determined to be negligible compared to the other terms in the HETP equation. On the other hand, extra‐column contributions, proportional to the square of the gas velocity, are of significant importance. This contribution is inversely proportional to the column length.
Pesticide residue analysis in food with CGC — study of long‐term stability by the use of different injection techniques
Authors: Müller Hans‐Martin , Stan Hans‐Jürgen 
Published: May 2005

AbstractAn experiment was designed to study the long‐term stability of analyses of pesticide residues in a complex food matrix using three different injection techniques. A spinach sample was spiked with five sulfur‐containing pesticides of varying volatility and thermolability: azinphos‐ethyl, dimethoate, methiocarb, ethiofencarb, and tri‐allate. Tri‐allate was selected as internal standard because of its thermal stability and its good chromatographic properties. Flame photometric detection resulted in chromatograms not subject to interference by peaks of compounds of the matrix. Starting with a clean and freshly, silanized injector an additional deactivation was found to occur on the first injection of a food sample resulting in an increased peak area for all pesticides in relation to tri‐allate. Highest long‐term stability was found with PTV injection. Best results for thermolabile carbamates were obtained using on‐column injection. However, they were prone to faster deterioration.
Cyclodextrins as chiral stationary phases in capillary gas chromatography. Part VII: Cyclodextrins with an inverse substitution pattern – synthesis and enantioselectivity
Authors: König Wilfried A. , Icheln Detlef , Runge Torsten , Pforr Ingo , Krebs Adolf 
Published: May 2005

AbstractTransferring the site of specific substitution of dipentylated cyclodextrins with methyl or acyl residues from the secondary 3‐hydroxyl group to the primary 6‐hydroxyl group was expected to provide new information on the mechanism of chiral recognition. The 3‐position points towards and the 6‐position points away from the cyclodextrin cavity which via inclusion complex formation is supposed to play a major role in chiral separation. The “inverse” 6‐O‐acyl‐2,3‐di‐O‐pentyl‐cyclodextrins displayed almost no enantioselectivity but the corresponding 6‐O‐methyl derivatives are a versatile supplement to the chiral capillary GC phases nowadays available. Among the compounds that could be enantiomerically resolved are alcohols, amino acids, alkyl halides, bicyclic ethers, acetals, olefins, other hydrocarbons and chiral pharmaceuticals.
Analysis of sucrose fatty acid esters by high temperature gas chromatography
Authors: Karrer Randolf , Herberg Hanna 
Published: May 2005

AbstractA commercially available high temperature GC system has been investigated to determine its suitability for the automated analysis of sucrose fatty acid esters. In comparison with conventional GC, the high temperature variety broadens the scope of the technique to encompass high molecular weight carbohydrate derivatives while maintaining high separation efficiency. Despite the broad range of polarities, simultaneous quantification of educts and sucrose fatty acid ester fractions is possible in one run, after derivatization. Chromatographic requirements, sample preparation, structure verification by direct chemical ionization mass spectrometry, and advantages and limitations of the high temperature GC‐analysis are discussed.
Use of mercuric resins for selective abstraction of mercaptans in capillary gas chromatography
Authors: Sun Jeffrey J. , Fritz James S. 
Published: May 2005

AbstractA small amount of mercuric non‐porous resin placed in the liner of the injection splitter of a gas chromatograph retains mercaptans but allows other organic sulfur and non‐sulfur compounds to be chromatographed normally: mercaptans in the gaseous state are retained by the mercuric resin. The method works well at 200°C but an increasing number of impurity peaks are observed as the temperature is increased to 250°C.
Quality control of vegetable oil methyl esters used as diesel fuel substitutes: Quantitative determination of mono‐, di‐, and triglycerides by capillary GC
Authors: Plank Christina , Lorbeer Eberhard 
Published: May 2005

AbstractVegetable oil methyl esters are increasingly being used as substitutes for petroleum‐based diesel fuels. Because the presence of triglycerides and partial glycerides in the fuel as a result of incomplete transesterification of vegetable oils can lead to serious engine problems, continuous quality control of the product is essential. A rapid gas chromatographic method has been developed for the quantitative determination of mono‐, di‐, and triglycerides in vegetable oil methyl esters.Prior to analysis, mono‐, and diglycerides were silylated with N,O‐bis(trimethylsilyl)trifluoroacetamide; tridecanoin was used as internal standard. Calibration was performed by analysis of standard solutions containing mono‐, di‐, and triolein: the calibration plots for mono‐ and diglycerides showed good linearity, whereas for triglycerides no linearity was observed for triolein concentrations below 0.05 mg/ml. When a non‐linear multi level calibration was employed for the quantitation of triglycerides, the method gave excellent quantitative results for mono‐, di‐, and triglycerides in vegetable oil methyl esters.
Calculation of retention factors in capillary electrochromatography from chromatographic and electrophoretic data
Authors: Vissers Johannes P. C. , Claessens Henk A. , Coufal Pavel 
Published: May 2005

AbstractRetention factors in capillary electrochromatography (CEC) were calculated by means of theoretically derived equations and experimentally determined parameters in microcolumn liquid chromatography and capillary zone electrophoresis. It was found that the retention factor of uncharged components in CEC was about 20% higher than was calculated. The derived equations do not take into account alteration of the nature of the stationary phase or distribution constant by the applied electric field. However, the influence of the electric field on the retention in CEC can be estimated. Individual field contributions could not be determined.
Low flow rate modifier addition in packed capillary column supercritical fluid chromatography
Authors: Ibañez Elena , Li Wenbao , Malik Abdul , Lee Milton L. 
Published: May 2005

AbstractA new method to accurately deliver small amounts (0.5 to 20 mol%) of modifier into CO2 was used to study the effects of three different modifiers (methanol, water, and formic acid) in packed capillary column SFC. The method allows the use of different modifiers, with minimal instrument modification. The effects of the different modifiers at different concentrations on retention and peak shape are shown by analyzing a polarity test mixture and a sample of free fatty acids.
Separation of polycyclic aromatic hydrocarbons with a C60 bonded silica phase in microcolumn liquid chromatography
Authors: Saito Yoshihiro , Ohta Hatsuichi , Terasaki Hiroshi , Katoh Yoshiyuki , Nagashima Hideo , Jinno Kiyokatsu , Itoh Kenji 
Published: May 2005

AbstractA chemically bonded C60 silica phase was synthesized as a stationary phase for liquid chromatography (LC) and its retention behavior evaluated for various polycyclic aromatic hydrocarbons (PAHs) using microcolumn LC. The results indicate that the C60 bonded phase offers selectivity different from that of octadecylsilica (ODS) bonded phases in the separation of isomeric PAHs. With the C60 phase, PAH molecules having a partial structure similar to that of the C60 molecule, e.g. triphenylene and perylene, were retained longer than with ordinary ODS stationary phases. The results also show that good correlation exists between the retention data with this C60 bonded phase and with C60 itself as the stationary phase.
The pure‐rotational Raman spectrum of disilane
Authors: Shotton K. C. , Lee A. G. , Jones W. J. 
Published: May 2005

AbstractFrom a study of the rotational Raman spectra of disilane and hexadeutero‐disilane the following rotational constants were determined: for Si2H6, B0 = 0.16998 ± 0.00003 cm−1; for Si2D6, B0 = 0.13796 ± 0.00004 cm−1. The rotational constants were used to provide values for the internuclear distances in these modecules.
Infrared and Raman spectra of trithiadiborolanes, SB(X)SB(X)S, with X  Cl, Br, I or Ch3
Authors: Sacher Robert E. , Siebert Walter , Nakovich John , Miller Foil A. 
Published: May 2005

AbstractInfrared and Raman spectra of the above four compounds have been obtained in the liquid and solid states down to 35 cm−1 (infrared) or to about 70 cm−1 (Raman). The results provide good evidence (but not rigorous proof) that the molecules are planar and have C2ν symmetry. The presence of boron isotopes causes splitting of some of the higher frequency bands. Assignments have been made for 57 of the 60 skeletal fundamentals of the 11B–11B isotopic molecules About ⅔ of these are reliable; the remainder are not well established. The S–S stretching frequency is at 449, 436, 425 and 479 cm−1 in the Cl, Br, I and CH3 compounds respectively.The planarity of the rings can be explained on the basis of bond angles alone, or on the postulate of an aromatic ring system. There is at present no other evidence to support the latter. The vibrational spectra provide no evidence about π bonding in these molecules.
Resonance Raman effect of anthracene in the pre‐resonance region
Authors: Schmid E. D. , Derner H. , Berthold G. 
Published: May 2005

AbstractThe Raman intensities (RI) of ten vibrations of Anthracene have been measured as a function of the excitation frequency using nine lines from an argon ion and a krypton ion laser. The intensities taken relative to those for a particular excitation frequency, S/S (v0), do not show uniform resonance behaviour. However uniformity arises, when the relative intensities are expressed on the same scale, and such ΔS/ΔS0 values may reflect the influence of frequency factors and varying percentage π‐dependence.
Analyse Vibrationnelle et Structurale en Série Aliphatique Saturée. I—Spectres de Vibration de l'Acide Malonique et de Ses Sels Alcalins en Solution Aqueuse
Authors: Maury Luc , Bardet Lucette 
Published: May 2005

AbstractVibrational spectra (Raman and infrared) of malonic acid, potassium hydrogen malonate and dipotassium malonate in aqueous solutions (H2O and D2O) were recorded from 250 to 4000 cm−1. The analysis of the polarisation ratio of the Raman lines had lead us to establish that the malonic acid belongs to the C1, the acid salt to Cs group. The potassium hydrogen malonate spectra, invalidate the existence of an intramolecular hydrogen bond suggested by thermodynamic data and show the characteristic vibrations of the simple COOH and COO− group. An assignment of the observed lines as fundamentals is proposed.
Raman scattering and vibrational dynamics of MnCl2·2H2O
Authors: Srivastava Bipin K. , Khandelwal D. P. , Bist H. D. 
Published: May 2005

AbstractThe laser excited Raman spectrum of MnCl2·2H2O has been reported in the 4000–150 cm−1 region and discussed in conjunction with the known IR spectra. The bands have been assigned to internal and librational modes of water and other lattice modes. It has been found that the correlation splitting parameter Δν/νmean is distinctly larger for the librational modes than for the internal modes of water. The increase in intensity of the ν1 over the ν3 band of water in passing from the free to crystal water state and the low intensity of the librational bands have been explained.
Investigation of broad molecular absorption bands with the help of line shape analysis in coherent Raman scattering experiments
Authors: Pfeffer M. , Lau A. , Werncke W. 
Published: May 2005

AbstractThe line shape observed in coherent Raman scattering (CRS) with excitation under conditions of electronic resonance is discussed, For the case of A‐type scattering, the complex Raman amplitude is related directly to the molecular one‐photon absorbance of the resonance transition concerned. The basis for this relation is transform theory, a method known from spontaneous resonance Raman scattering to relate the Raman excitation profile to the observed molecular absorbance. Features of the Raman amplitude, determining the observed line shapes for coherent anti‐Stokes Raman scattering (CARS) and for coherent Stokes Raman scattering (CSRS), are discussed qualitatively. The discussion considers two typical forms in which broad molecular absorption spectra of polyatomic molecules in the condensed phases appear, Inhomogeneous broadening leads to characteristic changes of the Raman amplitude in relation to molecular absorbance in the case of CSRS (formolecules in the electronic ground state), whereas for CARS the relation derived in the homogeneous broadened case remains valid. The special advantages of the CRS technique for determining the complex non‐Raman resonant (background) susceptibility from concentration dependence are demonstrated.
Herman‐wallis factors for Raman transitions of 1∑‐state diatomic molecules
Authors: Tipping R. H. , Ogilvie J. F. 
Published: May 2005

AbstractAccurate theoretical expressions for Herman‐Wallis factors for the pure rotational, fundamental and first two overtone vibration‐rotational bands have been derived. These are expressed for arbitrary rotational quantum numbers in terms of the Dunham potential parameters and the coefficients of a general operator represented by a power series expansion. The inclusion of higher order corrections in a consistent way reduces the discrepancy reported by previous workers for H2 between results obatined numerically and analytically. The present expressions are of sufficient accuracy to enable one to obtain precise experimental values for the anisotropy of the polarizability and its derivatives from an analysis of Raman line intensities.
Raman study of the high‐temperature phase transition of malonic acid
Authors: de Villepin J. , Limage M.‐H. , Novak A. , Toupry N. , Le Postollec M. , Poulet H. , Ganguly S. , Rao C. N. R. 
Published: May 2005

AbstractThe Raman spectra of the high‐temperature (α) phase of crystalline malonic acid, CH2(COOH)2, and its deuteriated derivative, CD2(COOD)2, have been investigated at 370 K in the wavenumber shift range 0–4000 cm−1. An assignment of the internal and external vibrations is given. Comparison of the infrared and Raman spectra of the α and β phases shows that the high‐temperature phase (α) consists of quivalent centrosymmetric dimer rings and that the corresponding space group is CC2/c with molecules occupyging C2 sites. The temperature dependence of various Raman lines, in particular those due to lattice modes, indicates that the phase transition is of first order and that during the transition, reorientation of the molecules about the c axis is strongly coupled with the low‐frequency torsional (γOH…O) and librational modes.
Raman and infrared spectra of crystalline cyanogen
Authors: Andrews Bruce , Anderson Anthony , Torrie Bruce 
Published: May 2005

AbstractRaman and infrared spectra of polycrystalline cyanogen, C2N2, at 20 K are reported. Multiplet structure of the intramolecular fundamentals is observed and interpreted in terms of a group theoretical analysis based on the known orthorhombic crystal structure. Seven of the eight predicted librational and five of the predicted six translational modes are observed in the low‐frequency regions of the Raman and infrared spectra, respectively.
Raman spectra of the lanthanide oxalates
Authors: Morris D. E. , Hobart D. E. 
Published: May 2005

AbstractRaman and infrared spectral data are presented for the trivalent lanthanide sesquioxalates, M2(C2O4)3 · nH2O, except the promethium complex, in the region from 100 to 4000 cm−1. These complexes were isolated by precipitation from aqueous solution using Na2C2O4. In addition, several commercially available oxalate complexes were examined. On the basis of nearly identical Raman spectral patterns, two distinct structural groups have been identified. The first group consists of the isostructural (monoclinic) decahydrates of La3+ through Er3+. For this group, a linear correlation is found for the frequencies of several skeletal stretching modes versus the lanthanide ionic radius. The second group consists of the isostructural (triclinic) hexahydrates of Er3+ through Lu3+. In agreement with existing x‐ray diffraction data, these vibrational data indicate structural differences between the hexa‐ and deca‐hydrates. In addition, unique vibrational spectral patterns have been obtained for what appear to be other hydrated forms of the oxalates of Ho3+, Er3+ and Lu3+, possessing structures different from those of the above hexa‐ and deca‐hydrates. For all of these complexes, the Raman data suggest that the oxalate ligand is tetradentate coordinated to two lanthanide ions. Thus, the structural differences undoubtedly result from the lanthanide contraction and changes in the disposition of coordinated and interstitial water molecules.
Calculation of anharmonic force constants for the CD3 group from the Raman spectra of (CD3)(CH3)3NI
Authors: Vidal Luis Sastre , Bertrán José FernáNdez 
Published: May 2005

AbstractThe anharmonic force constants for the CD3 group, W12(k122), W13(k133) and W23(k2233), were calculated by a method in which the only approximation is the neglect of the intrinsic intensities of the unperturbed transitions 2δs° and 2δa°. Using Raman data for (CD3)(CH3)3NI solutions, the calculated values of the anharmonic forces constants are W12 = 42.5 cm−1, W13 = 21.5 cm−1 and W23 = 9.4 cm−1.
Charge‐transfer and orientation effects of SERS from pyridine adsorbed on a silver electrode
Authors: Lin H. J. , Chou Y. C. 
Published: May 2005

AbstractExcitation profiles of the Raman modes of pyridine adsorbed on a silver electrode in sodium chloride electrolyte of different concentrations do not agree with expectation from the charge‐transfer model based on the dependence of the maximum voltage on the incident photon energies. The orientation of the adsorbed molecules might correlate with the position of the charge‐transfer band.
Raman spectra of some complexes containing methyldihalo‐ and dimethylhalo‐sulphonium cations: Isomerism in the dimethyl sulphide–bromine complex
Authors: Askew Herbert F. , Gates Peter N. , Muir Alan S. 
Published: May 2005

AbstractVibrational assignments for the skeletal modes of some complexes containing CH3SX2+ and (CH3)2SX+ (X = Cl, Br) have been made on the basis of their solid‐state Raman spectra and compared with any previous data. The stabilities of the parent CH3SX3 and (CH3)2SX2 compounds are discussed; two isomers of (CH3)2SBr2 were obtained under varying reaction conditions and assigned as ionic [(CH3)2SBr+Br−] and charge‐transfer [(CH3)2S → Br2] forms. The transition of the ionic (metastable) form to the more stable charge‐transfer form was monitored by differential scanning calorimetry. High‐frequency shifts occur in some fundamental modes of (CH3)2SBr+Br− when Br− is replaced with a polyatomic anion, analogous to those seen in halophosphonium complexes; this is rationalized in terms of anion‐cation interaction.
Vibrational spectra of trifluoromethylsulphenyl cyanide, CF3SCN
Authors: Altabef A. Ben , Cutin E. H. , Védova C. O. Della 
Published: May 2005

AbstractThe infrared spectra of trifluoromethylsulphenyl cyanide, CF3SCN, in the vapour phase and the Raman spectrum of the liquid were obtained and interpreted in terms of Cs symmetry. Assignment of 14 of the 15 fundamental vibrations is carried out. The valence force constants were calculated by a stepwise coupling method for the A′ species. These values compare favourably with results from previous calculations on related compounds.
Surface‐enhanced Raman scattering of 4‐picolylamine and its [Fe(CN)5]n− complexes
Authors: Temperini M. L. A. , Rubim J. C. , Sala O. , Jubert A. H. , Villalba M. E. Chacon , Aymonino P. J. 
Published: May 2005

AbstractThe SER spectra of the complexes [Fe(CN)5(4‐picolylamine)]3− and [Fe2(CN)10(4‐picolylamine)]6− adsorbed on a silver electrode were investigated. The analysis of the frequency shift of the CN stretching mode indicated that both molecules adsorb via one or more CN ligand groups. For potentials more positive than 0.0 V the CN stretching frequency for both complexes moves towards higher wavenumbers charcterizing the presence of Fe(III) over the surface. The SER spectra of 4‐picolylamine adsorbed on a silver electrode in solutions of pH 2.8, 6.5 and 10.3 were also investigated. From the data obtained it was concluded that 4‐picolylamine in solution at pH 6.5 and 10.3 adsorbs on the electrode through the nitrogen of the pyridine ring.
Surface‐enhanced Raman spectra of thiourea in acidic solutions
Authors: Kim Hyeongon , Kim Jong‐Jean 
Published: May 2005

AbstractSurface‐enhanced Raman scattering (SERS) of thiourea [SC(NH2)2] was studied in acidic solutions of 0.1 M H2SO4 and 0.1 M HCl. Very strong SERS bands of thiourea were observed in the acidic solutions, in contrast to very weak SERS spectra of thiourea in standard SERS solutions employing K2SO4 or KCl. Thiourea seems to have a strong and stable surface adsorption at a silver electrode in the acidic solutions where protonation and anionic co‐adsorption may enhance this surface stability of thiourea.