关键词：
Relative Standard Deviation;Polytetrafluoroethylene;PTFE;Inductively Couple Plasma Atomic Emission Spectrometry;Standard Reference Material
摘要：
Slurry sampling followed by electrothermal vaporization (ETV) was used as sample introduction technique in inductively coupled plasma atomic emission spectrometry (ICP-AES) for the direct determination of trace elements in food samples. A polytetrafluoroethylene (PTFE) emulsion was used as a fluorinating reagent to promote vaporization and the transportation of analytes. The main factors affecting the analytical signals were investigated in detail. Under optimum operating conditions, the detection limits (DL) for this method varied from 1.8 (Cu) to 215 ng/mL (Zn), while the relative standard deviations (RSD) were in the range 2.6% (Cu)-7.2% (Zn). The proposed method was successfully applied to the direct determination of trace amounts of V, Cu, Cr, Fe, Zn, and La in rice without any chemical pretreatment. The precision was evaluated by analyzing a standard reference material (tea leaves, GBW 07605) and comparing the results from this method with results obtained by pneumatic nebulization (PN) ICP-AES after the wet-chemical decomposition of the same sample.
摘要：
A procedure for the determination of trace elements in human hair has been proposed by electrothermal vaporization inductively coupled plasma optical emission spectrometry (ETV-ICP-OES) with slurry sampling. Slurry was prepared by immersing human hair with conc. HNO3 and then adding a polytetrafluoroethylene (PTFE) slurry, which was used as a chemical modifier for the improvement of vaporization characteristic of analyte. The slurry was homogenized with an ultrasonic vibrator before the measurement. The vaporization behaviour of the analytes in slurry and solution and the main influence factors for the determination were studied with the addition of PTFE systematically. Detection limits for this method varied from 0.033 µg g−1 (Cu) to 3.21 µg g−1 (Zn) with the relative standard deviations (RSDs) of 2.8–7.1%. The proposed method was successfully applied for the determination of trace elements (Cu, Mn, Cr, Fe, Zn, Cd and Pb) in human hair with minimum chemical pretreatment and aqueous calibration. The accuracy was checked by comparing the results of this method with those using pneumatic nebulization (PN) ICP-OES after a conventional acid decomposition of the same sample. In addition, the standard reference material of human hair (GBW 07601) was analysed with good agreement between the results from the proposed method and the certified values.
摘要：
The interactions between drug molecules and membrane were studied using the new chromatography stationary phase of liposome coated zirconia-magnesia. logK(s)(ZrO(2)-MgO) on this new chromatography for some drugs, compared with that on liposome coated silica chromatography and other reported data, fair correlations were observed between them when excluding effect of special adsorption. logK(s)(ZrO(2)-MgO) values for barbitalum, diazepam, benzene, benzocaine and toluene correlated well with corresponding values on liposome coated silica chromatography (R=0.99778, P<0.001; R=0.98229, P<0.003; R=0.9985, P<0.0001; R=0.99925, P<0.0001, pH value of mobile phase at pH 7.4, 7.0, 6.4 and 5.4, respectively). They also correlated well with the literature data on immobilized artificial membrane chromatography (R=0.99999, P<0.004 at pH 7.4) and liposome chromatography (R=0.99994, P<0.008) for procaine, lidocaine and bupivacaine. Liposome coated zirconia-magnesia chromatography can thus be used for studying drug-membrane interaction and prediction of drug absorption as another liposome chromatography method.
作者机构：
[Owens, FJ] Armament Res Dev & Engn Ctr, Picatinny Arsenal, NJ 07806 USA.;[Owens, FJ] CUNY Hunter Coll, Dept Phys
通讯机构：
[Owens, FJ] A;Armament Res Dev & Engn Ctr, Picatinny Arsenal, NJ 07806 USA.
关键词：
Hardness;Nanocomposites;Polymers magnetic materials;Conductivity
摘要：
Composites of polyacrylonitrile (PAN ) and single walled carbon nanotubes (SWNTs) as well as fluorinated SWNTs produced by evaporation of suspensions of PAN and SWNTs while being subjected to sonication are characterized. Raman measurements of the PAN/SWNT composites showed upward shifts of the tangential mode frequency of the SWNT compared to that of the pristine SWNT while in composites of the fluorinated SWNTs the tangential mode shifted down. These results are indicative of interaction between the PAN and the SWNT. Hardness measurements as a function of weight percent SWNTs indicated that composites made from the fluorinated SWNTs had larger tensile strengths than composites made from non functionalized SWNTs having the same number of carbon nanotubes. Composites of the non-functionalized SWNTs were highly conducting while those made of the fluorinated SWNTs were not.
摘要：
This paper presents analytic solutions for the flow field of inviscid fluid induced by uniformly and rigidly moving multiple helical vortex filaments in a cylindrical pipe. The relative coordinate system is set on the moving vortex filaments. The analytical solutions of the flow field are obtained on the assumption that the relative velocity field induced is time-independent and helically symmetrical. If the radius of the cylindrical pipe approaches infinity, these solutions are also available for unbounded space. The results show that both the absolute velocity field and pressure field are periodical in time, and may reduce to time-independent when the helical vortex filaments are immobile or slip along the filaments themselves. Furthermore, the solution of velocity field is reduced to Okulov's formula for the case of a single static vortex filament in a cylindrical pipe. The calculated locations of pressure peak and valley on the pipe wall agree with experimental results.
关键词：
metal ion;catalysis;PNPP;kinetics and mechanism
摘要：
The hydrolysis of PNPP was investigated in the presence and absence of Co(II), Cu(II), Ni(II), Zn(II), La(III) at 25 degrees C and ionic strength of 0.1 mol dm(-3). The results indicate that the spontaneous hydrolysis of PNPP was catalyzed by hydronium ion, hydroxide ion and water molecule, because of the existence of the pyridium nitrogen, while the metal ion catalyzed hydrolysis of PNPP at zero buffer concentration fulfills the equation: k(obsd) = Ka/[H+] + K-a (k(H) [H+] + k(0) + k(OH)K(W)/[H+]) showing that the reaction proceeds via nucleophilic attack by external Old on the metal ion complex of PNPP. The order of catalytic ability of different metal ions was interpreted by the stability of the complex structure relative to the structure of the ground-state intermediate, employing the method devised by Kurz for catalyzed reaction.
摘要：
Sinorhizobium fredii YC4B is a spontaneous mutant derivative of strain YC4 that is unable to nodulate soybeans. The second-largest plasmid of strain YC4B, termed pSfrYC4b (810 kb), was transferred to S. fredii HN01SR, a strain which contains three large indigenous plasmids (pSfrHN01a, pSfrHN01b and pSfrHN01c). Surprisingly, two stable indigenous plasmids (pSfrHN01a and pSfrHN01b) of strain HN01SR were cured simultaneously by the introduction of pSfrYC4b. Furthermore, a novel, unstable plasmid (pHY4) became visible in agarose gels. The electrophoretic mobility of plasmid pHY4 was slower than that shown by the cured plasmids, indicating that the molecular weight of the former is higher than that of plasmids pSfrYC4b and pSfrHN01b. Replication gene repC-like sequences were detected by polymerase chain reaction (PCR) on pSfrHN01a and pSfrYC4b, but not on pSfrHN01b. Sau3AI and PstI restriction patterns of the PCR-amplified repC-like sequences from HN01SR and YC4B were very similar.
摘要：
An aerodynamic evaluation method for internal epoxy coating in natural gas pipeline was presented by introducing the friction factor of flowing gas. Numerically calculated values of this factor from the Colebrook-White equation were compared with model experimental and field comparatively tested data. They show good agreement between the numerical and experimental results. Therefore, it proves that the Colebrook-White equation is available for evaluation of the epoxy coating in natural gas pipeline. With this method, the friction factors show a notable relative decrease rate up to 25% at Reynold's number of 4.32 x 10(7) for a pipe diameter of 1016 mm due to the application of the internal epoxy coating. (c) 2005 Elsevier B.V. All rights reserved.
摘要：
The glassy carbon electrode coated with electropolymerized methyl-red film, 1.2 x 10(-6) m in thickness, (PMRE) showed high sensitivity towards Hg(II) ions. PMREs were adopted to accumulate and detect H(II) ions in a pH 2.56 Britton-Robinson buffer solution. Cyclic voltammogram of the accumulated Hg species on PMREs exhibited an anodic wave at 0.64 V and a cathodic wave at 0.13 V, due to the oxidation of accumulated Hg species on PMREs and the reduction of Hg(II) ions in the solution, respectively. For this heterogeneous adsorption of Hg(11) ions onto PMREs, the maximum surface concentration, adsorption equilibrium, and Gibbs energy change were evaluated to be 5.12 x 10(-6) mol m(-2), 3.7 x 10(5) l mol(-1), and -30.1 kJ mol(-1), respectively. The anodic peak current at 0.64 V was linear with the concentration of Hg(H) ions in the range of 1.1 x 10(-10) to 1.1 x 10(-7) M with a detection limit of 4.4 x 10(-11) M. The proposed method was utilized successfully for the detection of Hg(II) ions in the lake water. (C) 2005 Elsevier B.V. All rights reserved.
