bluuebunny/crossref_metadata_2025_split huggingface dataset:
Novel column oven concept for cold spot large volume sample enrichment in high throughput temperature gradient capillary liquid chromatography
Authors: Holm Anders , Molander Paal , Lundanes Elsa , Greibrokk Tyge 
Published: August 2003

AbstractA novel column oven concept with an incorporated cold spot has been tailored for use in capillary liquid chromatography, allowing efficient injection of increased sample volumes by sub‐ambient temperature‐promoted solute enrichment. The column oven system consists of two horizontally connected temperature zones surrounding the packed capillary column. The oven is designed to allow horizontal sliding of the capillary column inside the column oven housing, enabling rapid transportation of the column inlet between the two temperature zones. This design eliminates the time consuming process of re‐cooling the oven after a temperature gradient, which is associated with other column ovens, providing the possibility of high throughput analyses. The cold inlet zone of the oven was operated at sub‐ambient temperatures where elution is suppressed to allow enrichment of large volumes of solutes dissolved in solvents usually associated with high eluting properties. The hot column oven zone allowed temperature‐programmed gradient action, but could also be operated isothermally resulting in a temperature step gradient. The oven was evaluated using the antioxidants Irgafos 168, Irgafos 168‐phosphate, and Irganox 1076 as model compounds using UV‐detection. A 3.5 μm Kromasil C18 0.25 mm ID×20 cm capillary column was used, while the mobile phase and the sample solvent was neat acetonitrile. The flow rate was 5 μL/min. Within‐assay precision and between‐assay precision of peak areas were in the range of 4.3–8.2% relative standard deviation (RSD). The retention time RSD in temperature gradient mode was 2%. The method was linear in the investigated range of 5–100 ng, displaying a correlation coefficient of 0.9995.
Direct high‐performance liquid chromatographic enantioseparation of α‐substituted proline analogues on a quinine‐derived chiral anion‐exchanger stationary phase
Authors: Péter Antal , Vékes Erika , Árki Anita , Tourwé Dirk , Lindner Wolfgang 
Published: August 2003

AbstractUse of a quinine‐derived chiral anion‐exchanger stationary phase for the direct high‐performance liquid chromatographic enantiomer separation of N‐protected unusual α‐substituted proline analogues is reported. The chromatographic conditions (eluent composition, pH, and buffer concentration) were varied to achieve optimal separation. The readily prepared 2,4‐dinitrophenyl derivatives were well separable, with good efficiency and high resolution. The elution sequences of the enantiomers of the derivatives were determined. Knowledge of the elution sequence allows identification of the configuration of the α‐substituted proline analogues in peptide epimers resulting from use of the racemates in the peptide synthesis. The method also proved suitable for determination of the enantiomeric purity of proline analogues obtained by asymmetric synthesis.
Investigation of the retention behaviour of steroids with calixarene‐based stationary phases by modern NMR spectroscopy
Authors: Skogsberg Urban , Händel Heidi , Gesele Elke , Sokoließ Torsten , Menyes Ulf , Jira Thomas , Roth Ulrich , Albert Klaus 
Published: August 2003

AbstractA separation of four structurally similar steroids was performed on two calix[8]arene based stationary phases. It was observed that two of the steroids had a reversed retention order when the columns were changed. This implies that two different retention mechanisms are taking place when the analytes are separated. In order to evaluate the mechanism responsible for the reversal of the retention order an extensive study of the interactions between the stationary phases and the analytes was undertaken. By performing a series of transferred NOESY measurements in the suspended state valuable information was obtained about the strengths of the interactions between the analytes and the stationary phases. The magnitudes of the integrals from the trNOESY measurements showed a good correlation with the k´ values obtained from the chromatographic evaluation. The retention mechanism is based mainly on hydrophobic interactions. However, the reversal of the elution order was mainly due to an additional π‐π interaction between one of the analytes and the stationary phase.
Characterization of complex mixtures of polyglycerol fatty acid esters using temperature and solvent gradients in packed capillary LC
Authors: Andersen Thomas , Holm Anders , Skuland Inger Lill , Trones Roger , Greibrokk Tyge 
Published: August 2003

AbstractA highly complex sample of polyglycerol fatty acid esters has been characterized using both temperature gradient and solvent gradient reversed‐phase packed capillary LC coupled to ELSD and ESI‐TOF‐MS. The techniques showed fairly similar performance in terms of selectivity and efficiency, providing a nice separation of not only the polyglycerol mono‐, di‐, tri‐ and tetra‐fatty acid esters, but also the non‐reacted polyglycerols. The different groups were identified by coupling the packed capillary LC system to a TOF‐MS using an electrospray interface, although the identification of the latest eluting groups in the temperature gradient separation was hampered due to significant column bleeding at elevated column temperatures. By calculating the peak areas in the ELSD chromatograms, the PGE sample was estimated to contain 20.2 ± 0.4 and 22.6 ± 0.5% non‐reacted polyglycerols, 44.4 ± 1.9 and 34.1 ± 1.4% mono‐fatty acid esters, 26.2 ± 1.5 and 27.9 ± 1.7% di‐fatty acid esters, 7.7 ± 0.7 and 12.6 ± 1.0% tri‐fatty acid esters, and 1.4 ± 0.2 and 2.8 ± 0.3% tetra‐fatty acid esters in temperature and solvent gradient mode (n = 3), respectively. The intra‐day precision of the retention times was 0.5–1.4% (n = 3) in the temperature gradient mode, while it was 0.3–1.7% (n = 3) in the solvent gradient mode.
Solid phase microextraction sampling and gas chromatography/mass spectrometry for field detection of the chemical warfare agent O‐ethyl S‐(2‐diisopropylaminoethyl) methylphosphonothiolate (VX)
Authors: Hook Gary L. , Kimm Gregory , Betsinger Geoffrey , Savage Paul B. , Swift Austin , Logan Tom , Smith Philip A. 
Published: August 2003

AbstractA rapid detection method for the chemical warfare nerve agent VX was developed using SPME and gas chromatography/mass spectrometry (GC/MS). Five commercially available SPME fiber coatings were evaluated to determine the optimal fiber coating and conditions for extraction. The use of silanized vials was found to be necessary to limit interaction of the basic tertiary amine component of VX with the acidic silanols present in standard glass vials. The polydimethylsiloxane (PDMS) fiber was ultimately selected for completion of this work with extractions being performed at 50°C. Clothing material was spiked in the laboratory with 1 μL of neat VX, placed in a sealed vial, and taken into the field for SPME sampling, using optimized conditions studied. GC/MS analysis was also completed in the field using van‐mounted instrumentation. With sampling and analysis completed in less than 20.0 minutes, detection of VX contamination was relatively rapid, especially considering the quality of the resulting data. The use of SPME also provides increased safety for the field analysis of VX since it does not require the handling of solvents for sample preparation and samples are not handled directly by the analyst.
Novel Polymerization of Fluorinated 2‐Vinylcyclopropane in Aqueous Solution via Cyclodextrin Complexes
Authors: Choi Soo Whan , Kretschmann Oliver , Ritter Helmut , Ragnoli Marina , Galli Giancarlo 
Published: August 2003

AbstractWe report on the first examples of the free radical polymerization of a fluorinated 2‐vinylcyclopropane 1 and its copolymerization with an alkyl 2‐vinylcyclopropane 2 in aqueous solution via their host‐guest complexation with a random methylated β‐cyclodextrin (RAMEB) using a water‐soluble initiator (VA50). Upon polymerization, the dethreaded cyclodextrin remained in water solution, whereas the water‐insoluble polymer precipitated out and was isolated. The polymers prepared exhibited mesophase behavior over a wide range of temperature. Both Tg and Ti of the copolymers increased linearly with the amount of fluorinated co‐units.Complexation of fluorinated vinylcyclopropane 1 with RAMEB and polymerization in water solution.magnified imageComplexation of fluorinated vinylcyclopropane 1 with RAMEB and polymerization in water solution.
Morphology and Crystallization Kinetics of Melt Miscible Polyolefin Blends
Authors: Müller Alejandro J. , Arnal Maria Luisa , Spinelli Ana Liz , Cañizales Edgar , Puig Cristian C. , Wang Howard , Han Charles C. 
Published: August 2003

AbstractBlends of copolymers of ethylene/hexene (9 CH3/1 000 C) and ethylene/butene (77 CH3/1 000 C) synthesized with metallocene catalysts were prepared by co‐precipitation from solution. A phase diagram for this blend had been obtained in a preceding work, where the blends were found to be miscible in the melt with a characteristic upper critical solution temperature (UCST). In this work, the successive self‐nucleation and annealing (SSA) thermal fractionation method revealed that both pure copolymers, even though they had been prepared by metallocene catalysis, displayed a very broad distribution of short chain branching. The thermal behavior of the pure copolymers and their blends revealed that co‐crystallization effects were present within each phase and that molecular fractionation during crystallization can prevail when the materials are slow cooled from the melt. A crystallization kinetics study was performed by differential scanning calorimetry (DSC) and it revealed a strong competition between crystallization and phase segregation. Upon cooling from a one phase melt, phase segregation precedes crystallization if the crystallization temperature (Tc) is high. On the other hand when low crystallization temperatures are employed, the amount of phase segregation that can be achieved before crystallization is limited. Transmission electron microscopy (TEM) allowed the observation of the lamellar morphology and their aggregation state. In specially prepared samples, the relative lamellar frequency of isothermally crystallized material was employed to ascertain whether the blend under consideration was within the one or the two phase region of the blends phase diagram.Crystallization half‐time for isothermally crystallized PEB/PEH blends quenched to the crystallization temperature from 170 °C.magnified imageCrystallization half‐time for isothermally crystallized PEB/PEH blends quenched to the crystallization temperature from 170 °C.
Crystallization and Melting Behaviors of PPC‐BS/PVA Blends
Authors: Zhang Zhihao , Mo Zhishen , Zhang Hongfang , Wang Xianhong , Zhao Xiaojiang 
Published: August 2003

AbstractThe isothermal crystallization and melting behaviors of poly(propylene carbonate) end‐capped with benzenesulfonyl/poly(vinyl alcohol) (PPC‐BS/PVA) blends over rich PVA composition range were first investigated by differential scanning calorimetry (DSC). PPC‐BS/PVA interaction parameter, χ12, calculated from equilibrium melting temperature depression was −0.44, revealing miscibility of PPC‐BS with PVA in the melt and favorable interactions. The temperature dependence of crystallization rate constant at initial crystallization stage was analyzed using the modified Lauritzen‐Hoffman expression. The chain width, a0, the thickness of a monomolecular layer, b0, the fold and lateral surface free energies, σe and σ, and the work of chain folding, q, for neat PVA were first reckoned to be 4.50 Å, 4.78 Å, 76.0 erg · cm−2, 8.81 erg · cm−2, and 4.70 kcal · mol−1, respectively. The values of σe and q for PVA in PPC‐BS/PVA blends exhibited a maximum in the neighborhood of 10/90 PPC‐BS/PVA, respectively.Kinetic analysis of the temperature dependence of crystallization rate constant at initial crystallization stage for neat PVA and PPC‐BS/PVA blends.magnified imageKinetic analysis of the temperature dependence of crystallization rate constant at initial crystallization stage for neat PVA and PPC‐BS/PVA blends.
Thermal‐Induced Crystal/Conformation Transformations in Syndiotactic Polystyrene Films Treated with Different Solvents
Authors: Sun Ya Sen , Woo E. M. , Wu Ming Chien 
Published: August 2003

AbstractSolution‐crystallized or solvent‐induced crystal forms and transitions of these crystals upon post‐annealing in solvent‐treated syndiotactic polystyrene (sPS) (films cast from o‐dichlorobenzene or immersed in 1,2‐dichloroethane, respectively) were investigated via wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and Fourier‐transform infrared (FTIR) spectroscopy. IR spectra in the frequency range of 720–820 cm−1, which is attributed to the CH out‐of‐plane bending of the phenyl ring for neat syndiotactic polystyrene (sPS) and their crystal/solvent complexes (sPS/o‐dichlorobenzene or sPS/1,2‐dichloroethane), were examined for the freshly as‐cast samples in comparison with those having been subjected to post‐annealing by heating to high temperatures. Three bands centered at approximately 779, 769, and 750 cm−1 were observed, the intensity and wavenumber being sensitive to the helical structural changes as a function of the annealing temperature. The band at 769 cm−1, being associated with the intramolecular interactions of the helical chains of the γ‐crystal, was used to confirm the formation of such a phase. The bands at 779 cm−1 and 769 cm−1 disappeared and the sharper band at 750 cm−1 remained upon further annealing above the γ → α′ transition temperature. Thus, by examining the temperature dependency as revealed in the IR spectra, the thermal‐induced phase transition from the δ‐ to an ordered γ‐ and then to an α′‐phase was successfully proven for the sPS/o‐dichlorobenzene complex. Similarly, the other sPS/1,2‐dichloroethane complex underwent transition (from a δ‐ to a disordered γ‐ and then to an α′‐phase) upon the same thermal treatments, except that the intermediate phase is a disordered γ‐phase.FTIR spectra in the frequency ranging from 720 to 820 cm−1 for the δ‐type sPS/o‐dichlorobenzene complex subjected to increase of the temperature by 5 °C steps in the range of 60–245 °C.magnified imageFTIR spectra in the frequency ranging from 720 to 820 cm−1 for the δ‐type sPS/o‐dichlorobenzene complex subjected to increase of the temperature by 5 °C steps in the range of 60–245 °C.
Positron Annihilation in Norbornene‐Ethylene Copolymers
Authors: Djourelov Nikolaj , Misheva Marijka , Zamfirova Galina , Benavente Rosario , Pérez Ernesto , Pereña José M. 
Published: August 2003

AbstractNorbornene‐ethylene amorphous copolymers with high content in norbornene are obtained with metallocene catalysts and present a high glass transition temperature. The size and concentration of the free‐volume holes of these copolymers, which affect to their gas barrier properties, has been studied by positron annihilation lifetime spectroscopy. The results of positron annihilation studies have shown that the microstructure of all samples is similar and they can be related to the dynamic mechanical parameters (temperatures and activation energies of the relaxations) as well as to the stress‐strain characteristics and microhardness of the copolymers. Moreover, it has been shown that in the case of the norbornene‐ethylene copolymers investigated the influence of the molecular rigidity on the glass transition temperature prevails over that of the pore dimensions.Apparent activation energies and reciprocal values of tan δ for the γ relaxation as functions of volumes of the holes determined at Tg −50 °C.magnified imageApparent activation energies and reciprocal values of tan δ for the γ relaxation as functions of volumes of the holes determined at Tg −50 °C.
Novel Labile Protected Amine Terpolymers for the Preparation of Patterned Functionalized Surfaces: Synthesis and Characterization
Authors: Braun Felix , Eng Lukas , Trogisch Sven , Voit Brigitte 
Published: August 2003

AbstractPhotolabile terpolymers have been designed and used to prepare thin organic films covalently attached to glass and silicon substrates. For this, terpolymers containing photolabile protected amino functions introduced by N‐(N‐nitroveratryloxycarbonylaminopropyl)methacrylamide as well as (trimethoxysilyl)propylmethacrylate and MMA as comonomers have been synthesized via free radical polymerization. The nitro group containing protecting group leads to a retardation of the free radical polymerization. But complete removal of non‐reacted monomer from the reaction product without gelation of the anchoring groups was achieved. Thin films from these terpolymers were structured imagewise by UV laser light irradiation in order to create defined functional areas at the template surface ready for further modification and attachment of nanoobjects. The selective deprotection was verified by UV‐imaging and selective modification reaction using fluorescence labeling.Area selective UV imaging of a AMINE‐P7 film; presentation of the changes in optical density after UV laser irradiation.magnified imageArea selective UV imaging of a AMINE‐P7 film; presentation of the changes in optical density after UV laser irradiation.
Effect of LiClO4 and LiCl Additives on the Kinetics of Anionic Polymerization of Methyl Methacrylate in Toluene‐Tetrahydrofuran Mixed Solvent
Authors: Dhara Mahua G. , Baskaran Durairaj , Sivaram Swaminathan 
Published: August 2003

AbstractThe kinetics of anionic polymerization of MMA has been studied at −78 °C in toluene‐THF (9:1 v/v) using 1,1′‐diphenylhexyl lithium as initiator in the presence of lithium perchlorate and lithium chloride as Lewis acid additives. The control of the polymerization is lost in the absence of additives as evident from the non‐linear first‐order time‐conversion plot and polymers with broad multimodal molecular weight distribution. The presence of LiClO4 and LiCl in 10:1 and 5:1 ratio, respectively, over the initiator brings about sufficient control, yielding polymers of narrow unimodal distribution throughout the polymerization. The reaction in the presence of the additives follows first‐order kinetics free of termination and transfer. Moreover, the order with respect to the active centers is found to be almost unity, which signifies a probable disaggregation of ion‐pairs to a single complexed propagating species.GPC elugrams at different conversions for MMA polymerization in the presence of LiClO4.magnified imageGPC elugrams at different conversions for MMA polymerization in the presence of LiClO4.
Aqueous Micelles from Supramolecular Graft Copolymers
Authors: Gohy Jean‐François , Hofmeier Harald , Alexeev Alexander , Schubert Ulrich S. 
Published: August 2003

AbstractAqueous micelles have been prepared from amphiphilic supramolecular graft copolymers, in which poly(ethylene glycol) (PEG) side chains were linked to a poly(methyl methacrylate) (PMMA) backbone via ruthenium(II)‐terpyridine complexes. Three different graft copolymers were investigated, in which the average number of PEG branches (constant length) and the length of the PMMA backbone were varied. The successful formation of micelles was proven by dynamic light scattering (DLS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). A good agreement was found between TEM and AFM observations, which show polydisperse spherical micelles. The hydrodynamic diameter measured by DLS was much larger, suggesting the formation of aggregates. No substantial difference in the micellar characteristic features was found between the three investigated samples.Schematic representation of the graft copolymer synthesis.magnified imageSchematic representation of the graft copolymer synthesis.
Molecular and Microdomain Orientation in Semicrystalline Block Copolymer Thin Films by Directional Crystallization of the Solvent and Epitaxy
Authors: Park Cheolmin , Rosa Claudio De , Lotz Bernard , Fetters Lewis J. , Thomas Edwin L. 
Published: August 2003

AbstractThe directional crystallization of crystallizable organic solvents and the subsequent epitaxial crystallization of crystalline blocks onto the surface of crystalline substrates in semicrystalline block copolymers, control both molecular chain orientation of the crystalline block and the microdomain structure of the block copolymer. Thin film of semicrystalline polystyrene‐block‐poly(ethylene‐alt‐propylene)‐block‐polyethylene (PS/PEP/PE) terpolymer and polystyrene‐block‐polyethylene (PS/PE) diblock copolymer, which both contain crystallizable polyethylene (PE) blocks, have been patterned using benzoic acid (BA) and anthracene (AN) as crystallizable solvents. The directional crystallization induces orientation of the microdomains and epitaxy, due to the crystallographic matching of unit cells between the crystalline PE blocks and the crystalline organic substrates, resulting in the development of highly aligned crystalline PE blocks. The orientation of the PE crystals onto the substrate is evidenced by selected area electron diffraction and bright field transmission electron microscope images. In the case of the PS/PEP/PE terpolymer, the process induces the PS cylinders to align parallel to the b axis of the BA crystals. Long crystalline PE lamellae are oriented edge‐on on the BA surface, with the b axis of PE parallel to the b axis of BA, and parallel to the PS cylinders. In the case of the PS/PE diblock copolymer, the PE cylinders are oriented perpendicular to substrate, packed on a hexagonal lattice. Each cylinder contains precisely one crystalline PE lamella oriented edge‐on on the substrate. When BA is used, the PE lamellae inside cylinders are oriented with the b axis parallel to the b axis of BA crystals. When AN is used, due to the different epitaxial relationship between PE block and AN crystals, the PE lamellae are oriented along two equivalent directions, with the c axis parallel to the [110] and $\left[ {1\bar 10} \right]$ direction of AN crystals.Schematic model of the final microstructure generated by combination of the directional crystallization and epitaxy.magnified imageSchematic model of the final microstructure generated by combination of the directional crystallization and epitaxy.