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21.
Matoušek T Hernández-Zavala A Svoboda M Langrová L Adair BM Drobná Z Thomas DJ Stýblo M Dědina J 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008,63(3):396-406
An automated system for hydride generation - cryotrapping- gas chromatography - atomic absorption spectrometry with the multiatomizer is described. Arsines are preconcentrated and separated in a Chromosorb filled U-tube. An automated cryotrapping unit, employing nitrogen gas formed upon heating in the detection phase for the displacement of the cooling liquid nitrogen, has been developed. The conditions for separation of arsines in a Chromosorb filled U-tube have been optimized. A complete separation of signals from arsine, methylarsine, dimethylarsine, and trimethylarsine has been achieved within a 60 s reading window. The limits of detection for methylated arsenicals tested were 4 ng l(-1). Selective hydride generation is applied for the oxidation state specific speciation analysis of inorganic and methylated arsenicals. The arsines are generated either exclusively from trivalent or from both tri- and pentavalent inorganic and methylated arsenicals depending on the presence of L-cysteine as a prereductant and/or reaction modifier. A TRIS buffer reaction medium is proposed to overcome narrow optimum concentration range observed for the L-cysteine modified reaction in HCl medium. The system provides uniform peak area sensitivity for all As species. Consequently, the calibration with a single form of As is possible. This method permits a high-throughput speciation analysis of metabolites of inorganic arsenic in relatively complex biological matrices such as cell culture systems without sample pretreatment, thus preserving the distribution of tri- and pentavalent species. 相似文献
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ÜMMÜHAN OCAK HALIT KANTEKIN YAŞAR GÖK H. BASIR ŞENTÜRK 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(1-2):87-91
The selective liquid–liquid extraction of various transition metal cations from the aqueous phase to the organic phase was carried out using a 14-membered N2O2S2-macrobicycle. Metal picrates such as Pb2+, Co2+, Zn2+, Ni2+,Cu2+ and Cd2+ were used in this extraction studies. It was found that the ligand showed moderate selectivity towards Pb2+ only among the other metals. The extraction constant (log K
ex) was determined to be 13.8 for Pb2+ complex. 相似文献
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The formation of discrete carbonaceous particles has been investigated for a conventional synthetic ester-based lubricant
degraded in thermal and thermal–oxidative environments. Experimental factors included oxidative and nonoxidative environments,
high and low humidities, and the presence or lack of a metal catalyst surface, with all samples generated at 250 °C. Characterization
performed for changes in antioxidant content, IR spectroscopy, molecular weight, total acid number, viscosity, and uv/vis
absorbance spectrometry were used to determine the influences of the aforementioned variables on the rates of oil degradation
and formation of high-molecular-weight species. Discrete carbonaceous particle formation was analyzed using Einstein's relationship
for the viscoelastic behavior of particles in Newtonian fluids and by calculating associated radii of gyration. This viscoelastic
behavior of the particles in solution is used to demonstrate how the absorption behavior of the carbonaceous degradation products
tracks the discrete particulate species. The results show the formation of particulate species to be diffusion-limited after
antioxidant depletion, and optical absorption analysis is shown to be a viable technique for monitoring the formation of discrete
carbonaceous particles during lubricant degradation.
Received: 29 February 2000/Accepted: 3 January 2000 相似文献
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Development of a new lectron-recoil ion/photon coincidence setup for investigating some of the electron induced collision processes, such as electron bremsstrahlung, electron backscattering,
innershell excitation and multiple ionization of target atoms/molecules in bombardment of electrons having energies from 2.0
keV to 30.0 keV with solid and gaseous targets is described. The new features include the use of a compact multipurpose scattering
chamber, a time-of-flight spectrometer for detection of multiply charged target ions, a 45°-parallel plate electrostatic analyzer
for measuring energy and angle of the ejected electrons, a room temperature high resolution Si-PIN photo diode X-ray detector
for counting the collisionally induced photons, a coincidence data acquisition system consisting of a 200 MHz Pentium based
8K-multichannel analyzer and a standard network of a fast/slow coincidence electronics. In particular, the details of design,
fabrication and assembly of indigenous components employed in the setup are presented. Selected experiments planned with the
setup are mentioned and briefly discussed. A report on performance, optimization, efficiency, time resolution etc. of the
time-of-flight (TOF) spectrometer and that of the 45°-parallel plate electrostatic analyzer (PPEA) is presented. Test spectra
of electron-recoil ion coincidences, energy distribution of ejected electrons and characteristic plus non-characteristic X-ray
spectrum are illustrated to exhibit the satisfactory performance of the developed setup. 相似文献
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