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91.
H. W. Gonell A. Blackie N. E. Edlefsen E. Kahane S. W. Parr P. F. Thompson C. W. Correns J. R. Bailey R. E. Remington J. F. Mc Clendon H. von Kolnitz R. G. Turner Minna Z. Weeks G. P. Baxter E. R. Bishop C. B. Dollins H. Starke K. Højendahl R. Jacquemain E. A. Werner E. André A. Okáč H. T. S. Britton B. M. Wilson 《Analytical and bioanalytical chemistry》1934,98(7-8):259-266
92.
A
method was developed for the quantification of low levels of amorphous content
in maltitol with StepScan DSC. The method was based on the fact that the change
of specific heat at the glass transition is linearly proportional to the amorphous
content. The influence of different measurement parameters of StepScan DSC
was evaluated and two different calibration heating rates were tested. Synthetic
mixtures with various proportions of crystalline and amorphous maltitol were
prepared. Two different measurement methods were compared and the linear regression
between ΔCp
and amorphous content was obtained. The limit of detection (LOD) and the limit
of quantification (LOQ) values were for the fictive temperature 0.24% (amorphous
content) and 0.81% and for the half point temperature 0.27 and 0.92%, respectively,
(method 1) and for the fictive temperature 0.18 (amorphous content) and 0.61%
and for the half point temperature 0.16 and 0.52%, respectively (method 2).
Very low determination limits for the quantification of amorphous content
could be attained with the StepScan DSC method. However, the realistic limit
of quantification was somewhat higher (about 3%) because of noise in the StepScan
measurement. The main advantage of the StepScan DSC method for quantification
of amorphous content was that the glass transition and relaxation peaks are
separated into different curves and the interpretation becomes easier. 相似文献
93.
Mercedes Vázquez Johan Bobacka Minna Luostarinen Kari Rissanen Andrzej Lewenstam Ari Ivaska 《Journal of Solid State Electrochemistry》2005,9(5):312-319
Potentiometric ion sensors have been prepared by galvanostatic electrosynthesis of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with p-sulfonated calix[4]arene (C[4]S) and p-methylsulfonated calix[4]resorcarenes (Rn[4]S) with alkyl substituents of different chain length (R1=CH3; R2=C2H5; R3=C6H13). The bowl-shape of these doping ions makes them suitable as ionic recognition sites, and their bulky character is expected to prevent them from leaching out of the conducting polymer membrane. For comparison, sensors based on PEDOT doped with poly(styrene sulfonate) (PSS) and poly(vinyl sulfonate) (PVS) were also constructed. The resulting GC/PEDOT electrodes were conditioned in 0.01 mol L–1 AgNO3 and their performance as Ag+ ion-selective electrodes (ISEs) studied. Results reveal that selectivity and lifetime of the electrodes is affected by the doping anion structure, although all electrodes show selectivity towards Ag+ ions. Interaction of Ag+ with sulfur atoms present in the conducting polymer backbone is considered to be the main reason for this behavior. A second set of electrodes was constructed and conditioned in 0.1 mol L–1 KCl. These electrodes were tested in chloride solutions of quaternary ammonium cations, showing that C[4]S and R2[4]S exhibit significant sensitivity towards pyridinium.Dedicated to Professor György Horányi on the occasion of his 70th birthday in recognition of his outstanding contributions to electrochemistry 相似文献
94.
Kristenson EM Korytár P Danielsson C Kallio M Brandt M Mäkelä J Vreuls RJ Beens J Brinkman UA 《Journal of chromatography. A》2003,1019(1-2):65-77
Different cryogenic and a heated GC x GC modulator(s) were evaluated and compared for the analysis of high-boiling halogenated compounds. The cryogenic modulators investigated were: (i) the longitudinally modulated cryogenic system; (ii) the liquid-nitrogen-cooled jet modulator (KT2001); (iii) a dual-jet CO2 modulator (made in-house); (iv) a semi-rotating cryogenic modulator (made in-house) and (v) a CO2 loop modulator (KT2003); the heated modulator was the slotted heater system (sweeper). Each modulator was optimised with respect to analyte peak widths at half height in the second-dimension. n-Alkanes, chlorinated alkanes, polychlorinated biphenyls (PCBs) and fluorinated polycyclic aromatic hydrocarbons (F-PAHs) were used as test analytes. The flow rate of the coolant was found to be an important parameter, i.e. the flow rate of the gaseous nitrogen in the KT2001, and of the liquid CO2 in the other cryogenic modulators. For the slotted heater the stroke velocity and pause time were important parameters. This modulator had a limited application range in terms of temperature due to a necessary 100 degrees C difference between sweeper and oven temperature. All cryogenic modulators were found to be suitable for the GC x GC analysis of high-boiling compounds, but the CO2 modulators are to be preferred to the KT2001 due to a wider application range and slightly narrower peaks. As regards the performance of three commercially available electron-capture detectors (ECDs), the aim was to obtain narrow peak widths in GC x GC, i.e. to avoid band broadening caused by the cell volume. The most important parameters were the flow rate of the make-up gas and the detector temperature which both should be as high as possible. Comparison of analyte peak widths obtained with ECD mode and flame ionisation detection (FID) showed that all ECDs exhibited band broadening compared to the FID. The narrowest peaks were obtained with the Agilent micro-ECD, which has a cell volume of only 150 microl. 相似文献
95.
Ruthenium complexes with dipyridophenazine (dppz) type ligands have several characteristics that make them good candidates for use as luminescence probes for hydrophobic environments. Most studies have concerned DNA intercalation, but also lipid membrane fluidity and liposome orientation have been assessed. We report here dipyridophenazine derivatives ([Ru(phen)2dppz]2+) substituted with one or two alkyl ether chains of different lengths aimed at finding the optimum substitution for a high quantum yield when bound to a phospholipid membrane bilayer. The orientation of membrane bound molecules is studied using flow linear dichroism (LD) with phospholipid vesicles as membrane models. LD, excitation anisotropy, steady state luminescence and excited-state lifetime measurements are used to quantitatively investigate the insertion and orientation of the complexes in the vesicles. All complexes are inserted with their long axis of the dppz moiety mainly parallel to the lipid chains, and the degree of orientation is comparable to that of the orientation probe retinoic acid. The ruthenium "head group" with its positive charge functions as a buoy at the water-membrane interface while the hydrophobic chain part embeds the complex down into the bilayer. The complex with two hexyl ether substituents (named D6) has the optimal chain length regarding membrane insertion and orientation, and together with the highest quantum yield, is the best luminescence membrane probe in the two series. 相似文献
96.
Gold is designated as the noblest metal because of its chemical inertness. It is known to dissolve in cyanide solutions in the presence of air or H2O2 or in halogen-containing solutions, aqua regia being the most famous example. Herein, we report a unique thiol, especially 4-pyridinethiol (4-PS), assisted dissolution of Au in alcohol solutions. Although dissolution was found to be very selective for pyridinethiols, such a phenomenon is astonishing since thiols are commonly used as etch resists for Au and even 4-PS is extensively used as a surface modifier for Au. To gain further understanding of the dissolution process, the influence of the reaction conditions was extensively studied. On the basis of the obtained results, a mechanism for the dissolution reaction is proposed. Fascinatingly, by tuning of the reaction conditions, this phenomenon can be applied in selective preparation of self-supporting nanometer-thick Au foils. 相似文献
97.
Mass transfer from the first-dimension to the second-dimension column in comprehensive two-dimensional gas chromatography (GC x GC) is normally quantitative, which means that the peak areas produced by GC x GC are equal to those obtained in one-dimensional gas chromatography (GC). In view of this relationship, it was investigated whether normal GC calibration could be used to quantify compounds analysed by GC x GC. Quantification of polycyclic aromatic hydrocarbons (PAHs) in sediment was used as a test case. It was concluded that more laborious and time-consuming GC x GC area calibration can be replaced by GC area calibration if separation quality and quantity prerequisites are met. 相似文献
98.
Zhen-Yu Yin Ching S. Chang Minna Karstunen Pierre-Yves Hicher 《International Journal of Solids and Structures》2010,47(5):665-677
Experimental evidences have shown deficiencies of the existing overstress and creep models for viscous behaviour of natural soft clay. The purpose of this paper is to develop a modelling method for viscous behaviour of soft clays without these deficiencies. A new anisotropic elastic–viscoplastic model is extended from overstress theory of Perzyna. A scaling function based on the experimental results of constant strain-rate oedometer tests is adopted, which allows viscoplastic strain-rate occurring whether the stress state is inside or outside of the yielding surface. The inherent and induced anisotropy is modelled using the formulations of yield surface with kinematic hardening and rotation (S-CLAY1). The parameter determination is straightforward and no additional experimental test is needed, compared to the Modified Cam Clay model. Parameters determined from two types of tests (i.e., the constant strain-rate oedometer test and the 24 h standard oedometer test) are examined. Experimental verifications are carried out using the constant strain-rate and creep tests on St. Herblain clay. All comparisons between predicted and measured results demonstrate that the proposed model can successfully reproduce the anisotropic and viscous behaviours of natural soft clays under different loading conditions. 相似文献
99.
100.