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101.
A novel flow-injection analysis (FIA) system has been developed for the rapid determination of the volatile acidity of some
fermentation products like vinegars and juices. The proposed method is based on the diffusion of volatile acids, mainly acetic
acid, across a PTFE gas-permeable membrane from an acid stream into an alkaline stream, and the acids trapped in the acceptor
solution are determined online by a bulk acoustic wave impedance sensor based on changes in the conductivity of the solution.
It exhibited a linear frequency response up to 10 mmol · L–1 acetic acid with a detection limit of 50 μmol · L–1, and the precision was better than 1% (RSD) at a through-put of 72 h–1. The effects of operating voltage for the detector, cell constant of the electrode, composition of acceptor stream, flow
rates and temperature on the FIA performance were also investigated.
Received: 2 June 1997 / Revised: 7 July 1997 / Accepted: 12 July 1997 相似文献
102.
[reaction: see text] The synthesis of allocyathin B(3) from an advanced intermediate possessing the ring system and relative stereochemistry but lacking the isopropyl and hydroxymethyl groups is reported. The isopropyl group was introduced by radical cyclization of a methyl propargyl acetal of an alpha-bromo ketone, and the hydroxymethyl group was generated by Pd-catalyzed carbonylation of a vinyl triflate. The route provides functionalized intermediates that could allow access to more complex members of the cyathin family of diterpenes. 相似文献
103.
Qiao Y Galvosas P Adalsteinsson T Schönhoff M Callaghan PT 《The Journal of chemical physics》2005,122(21):214912
Diffusion exchange of dextran with molecular weights 4.4 and 77 kDa through polyelectrolyte multilayer (PEM) hollow capsules consisting of four bilayers of polystyrene sulfonate/polydiallyldimethylammonium chloride has been investigated using two-dimensional nuclear-magnetic-resonance methods: diffusion-diffusion exchange spectroscopy (DEXSY) and diffusion-relaxation correlation spectroscopy (DRCOSY). Results obtained in DRCOSY experiments show that the diffusion process of dextran 77 kDa exhibits an observation time dependence suggesting a diffusion behavior restricted by confinement. We find evidence for both single capsule and capsule aggregate states, with a partitioning of the 77-kDa dextran between the free and capsule states much larger than that suggested by volume fraction alone. Results from DEXSY experiments show that dextran 77 kDa is in diffusive exchange through the capsules with an exchange time of around 1 s. In contrast, the capsules have no detectable influence on the diffusion process of the dextran 4.4 kDa. This quantitative information may be used in designing PEM capsules as drug carriers. 相似文献
104.
Honying M Han H Qiao C Richardson NV Yue W Jianhua Z Haiyang L Pimo H Shining B 《The Journal of chemical physics》2004,121(14):6972-6977
The structure of perylene adsorbed on Ru(0001) surface has been studied by ultraviolet photoemission spectroscopy (UPS) and low-energy electron diffraction. An ordered p(4x4) structure is observed from a monolayer (about 4 A thickness) of the perylene on Ru(0001) surface. UPS measurements show the molecular features, from the perylene multiplayer, between 2 and 10 eV below the Fermi level. Angle-resolved ultraviolet photoemission spectroscopy measurements suggest that the perylene molecular plane is parallel to the substrate. Temperature dependent UPS measurements show that the perylene multilayer is stable on Ru(0001) surface up to 125 degrees C. The desorption of the multilayer and the decomposition of the monolayer are observed above 125 degrees C. 相似文献
105.
106.
Solubility of methane in octane + ethanol was measured at temperatures ranging from 303.15 K to 333.15 K and pressures ranging
from 2.60 MPa to 12.01 MPa. Experimental data were analyzed using the Soave-Redlich-Kwong equation of state with three types
of mixing rules, and the estimated average deviation from the experimental solubility data was less than 3.5 %. 相似文献
107.
Xiaoji Cao Jingfang Qiao Liping Wang Xuemin Ye Lebin Zheng Nan Jiang Weimin Mo 《Rapid communications in mass spectrometry : RCM》2012,26(7):740-748
A powerful ionic liquid‐based ultrasonic‐assisted extraction (ILUAE) method combined with ultra‐performance liquid chromatography coupled to electrospray ionization quadrupole time‐of‐flight tandem mass spectrometry (UPLC/ESI‐QTOFMSn) was employed in the rapid simultaneous screening of iridoid glycosides, phenylethanoid glycosides, and cucurbitacin glycosides from P. scrophulariiflora. The ILUAE procedure was optimized over several ultrasonic parameters, including the ultrasonic power, concentration of the ionic liquid, and solid–liquid ratio. A comparison with conventional heat‐reflux extraction and regular UAE demonstrated that the optimized approach yielded a high extraction efficiency (Picroside I, 2.84%; Picroside II, 3.57%; 6‐O‐E‐feruloyl catalpol, 2.20%) within a short extraction time of 30 min. Negative ion mode ESI‐QTOFMS2 analysis of the fragmentation reactions of the [M–H]– ions was conducted to characterize the diagnostic ions related to the glycosyl moieties, aglycone units, and the type and substituted position of the ester groups. Interestingly, the positional isomers of the iridoid glycosides could be easily discriminated based on the characteristic ions. A total of 15 glycosides, including three groups of iridoid glycoside isomers and two groups of phenylethanoid glycoside isomers, were conveniently identified within 13.5 min. Moreover, 6'‐O‐vanilloyl catalpol was identified in P. scrophulariiflora for the first time. The method developed here was further validated by measuring the recovery, correlation coefficient (R2), and reproducibility (RSD, n = 5) of three iridoid glycosides: 89.60%–109.02%, 0.9991–0.9998, and 0.93%–1.44%, respectively. This study demonstrated the capabilities of ILUAE combined with UPLC/ESI‐QTOFMSn for the rapid screening of glycosides in P. scrophulariiflora. This method offers an approach to similar studies on other natural plants. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
108.
Mei Tian Huan Huan Sun Xiao Wei Tian Zhi Xin Xu Feng Qiao Wang Dan Shu Yao 《Liquid crystals》2013,40(3):298-308
A series of side-chain liquid crystal (LC) polysiloxanes were synthesised with Poly(methylhydrogeno)siloxane, 4?-(undec-10-enoyloxy) biphenyl – 4 – yl 4- (trifluoromethyl) benzoate (Mth) and a chiral nematic (N*) LC monomer 1-allyl 10-(cholesteryl)-decanedioate (Mch). The chemical structures and LC properties of the monomers and polymers were characterised by FTIR, 1H-NMR, differential scanning calorimetry, thermogravimetric analysis, POM and X-ray diffractometer. Mch is monotropic N* LC. The homopolymer derived from monomer Mch is enantiotropic N* LC. Monomer Mth is a smectic A liquid crystal. The copolymers derived from Mch and Mth are N* LCs. The temperatures at which 5% weight loss occurred are greater than 300°C for all the fluoro-containing polymers, and the residue weights of the samples at 600°C increased slightly as the content of trifluoromethyl mesogens increased in the polymers. The glass transition temperatures of the polymers increased as trifluoromethyl mesogens increased, too. The N*–I phase transition temperatures show a negative deviate from ideal or linear behaviour. The values of the enthalpy changes for the cholesteryl containing polymers are rather low and this is attributed to the biaxiality of cholesteryl moiety which tends to reduce the change in the orientational order at the N*–I transition. Compared to the monomers, the polymers show wider mesophase region. 相似文献
109.
A new mesogen, 3,4,5‐tris(11,11,12,12,13,13,14,14,15,15,16,16,16‐tridecafluoro‐hexadecyloxy)benzoic acid, with a thermotropic cubic phase was synthesized. The phase behaviour of the fluorinated compound and its corresponding non‐fluorinated analogue was investigated by differential scanning calorimetry, polarizing optical microscopy, and synchrotron small‐angle X‐ray diffraction. The fluorinated compound, which contains three partially perfluorinated alkoxy moieties and one carboxylic acid group capable of forming hydrogen bonding, exhibits a very interesting sequence of isotropic, cubic and hexagonal columnar phases, whereas its non‐fluorinated compound does not have a liquid crystalline phase. The cubic phase exists over a wide temperature range (from ~200°C to ~30°C on cooling) and is hence amenable to various physical measurements and potential applications. The ability to self‐assemble molecules into ordered superstructure via both partially perfluorinated chains and hydrogen bonding provides new insight for the development of novel liquid crystalline materials. 相似文献
110.
Hongxia Guo Yuechun Qiao Guohua Liu Jingqing Gao 《Russian Journal of Electrochemistry》2013,49(4):396-399
Single-phased nanosized LiFePO4 with thinner thickness along [010] crystallographic direction were successfully fabricated under solvothermal condition by using glycerol as co-solvent. The as-obtained product with thinner thickness is beneficial for fast migration of Li ions in the olivine-structured LiFePO4, hence exhibiting excellent electrochemical performance. 相似文献