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71.
Effkemann S Brødsgaard S Mortensen P Linde SA Karst U 《Fresenius' Journal of Analytical Chemistry》2000,366(4):361-364
A new method for the determination of peroxyacetic acid (PAA) in gas phase samples is described. It is based on the oxidation of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate) by PAA with formation of a radical cation which is characterized by four strong absorption maxima between 405 nm and 810 nm. These allow for sensitive spectrophotometric determination of the peracid. The selectivity of the method towards hydrogen peroxide is strongly dependent on the sampling method used. Impinger sampling and sampling based on the use of coated solid sorbents (test tubes) was performed. Limits of detection are 10(-8) mol, limits of quantification are 5 x 10(-8) mol, the linear range consists of 1.5 concentration decades in both cases. Using ABTS-coated test tubes above 1 x 10(-7) mol, direct reading of the results is possible and may be used as rapid screening method for the PAA concentration. 相似文献
72.
From a Cs doped Fe2O3-V2O5 (Fe:V=1.4) catalyst exhibiting an inhomogeneous composition after calcination, three different fractions have been separated by visual inspection. One fraction has been found to consist of mainly α-Fe2O3, another one of mainly FeVO4. The third fraction (S1 in the text) is the catalytically most active fraction containing besides both of the former components an amorphous phase of FexVyOz and also the dopant. By combining the results from transmission and conversion electron Mössbauer spectra it has been concluded that the amorphous component is enriched in the surface region of the crystallites of the catalyst. In addition, the formation of a thin surface layer of iron sulfide (Fe1?xS) on the third fraction has been identified. This sulfide is assumed to be formed during calcination from Cs2SO4 used for the preparation of the catalyst. 相似文献
73.
Wolfgang Schwack Bernd Brüger Steven Nyanzi 《Analytical and bioanalytical chemistry》1995,351(2-3):297-300
The differential pulse-polarographic (DPP) determination of both CS2 and COS gases, after their absorption in a methanolic piperidine reagent and the subsequent application of this technique to the residue analysis of dithiocarbamate fungicides is described. Rectilinear calibration curves for both CS2 and COS in the respective regions of 1.5–9.2 and 2.1–12.6 μmol/l were obtained. The DPP method has been successfully applied to the determination of thiram residues on apples after a hot acid hydrolysis of the fruits. 相似文献
74.
C. Bréchignac Ph. Cahuzac M. de Frutos P. Garnier 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,42(4):303-307
Mixed lithium-lithium oxide aggregates are experimentally obtained from unimolecular evaporative cascades starting at metal rich Li p + (Li2O)n species and ending with the stoichiometric limit Li+(Li2O)n, for several sizes of the oxide part (Li2O)n with 0 ≤ n ≤ 8. The results show evidence of the vanishing of the properties of the quantum metallic droplet i.e. shell closing and odd-even alternation, portrayed in the dissociation energy, with increasing size of the oxide component. The competition between monomer and dimer lithium evaporation from the heated metal rich Li p + (Li2O)n species points out the influence of the perturbation induced by the oxide component on the mixed metal oxide clusters. 相似文献
75.
Erwin Brüning 《Communications in Mathematical Physics》1978,58(2):167-194
The problem of uniqueness of monotone continuous linear extensions of $$T_{(2N)} = \{ 1,T_1 ,...,T_{2N} \} \in E'_{(2N)} = \prod\limits_{n = 0}^{2N} {E'_n } $$ is solved. A characterization of a relativistic QFT in terms of finitely many VEV's is derived. All results are illustrated by an explicit discussion of the extension problem for special cases ofT (4)={1,0,T 2,T 3,T 4}. This discussion contains explicitly necessary and sufficient conditions onT (4) for the existence of minimal extensions and some convenient sufficient conditions. 相似文献
76.
77.
The adsorption isotherms of the binary mixtures of ethanol/n-Octane, ethanol/n-hexadecane and n-octane/n-hexadecane onto the activated carbon TA 95 were measured at 278 K, 288 K, 298 K and 308 K and described with mathematical functions. About 300 experimental values of the adsorption excess of the ternary mixture ethanol/n-octane/n-hexadecane onto activated carbon TA 95 at 298 K were measured by gas chromatography inside the ternary triangle. The ternary miscibility gap was determined at three temperatures. A good representation of the ternary data and the calculated activity coefficients (using the UNIFAC model) in three-dimensional space was possible with the help of transformation of coordinates. It was possible, too, by utilization of the conception of the quasi two-component representation of the mole fractions with and without miscibility gap. Several influencing factors on ternary adsorption isotherms were discussed for the system ethanol/n-octane/n-hexadecane/TA 95. 相似文献
78.
The effects of four wash procedures on the concentration of chromium in a pooled sample of human scalp hair are compared. The wash solutions examined are Triton X-100, sodium lauryl sulphate, acetone, and a mixture (1 + 1) of hexane and ethanol. The plateaux reached for hair chromium concentration are functions of the number of washings, and are characteristic for each wash solution. The wash procedure recommended involves two 20-min washes with aqueous 1% sodium lauryl sulphate solution after a hexane rinse. 相似文献
79.
Lorenz V Fischer A Jacob K Brüser W Edelmann FT 《Chemistry (Weinheim an der Bergstrasse, Germany)》2001,7(4):848-857
The preparation and structural characterization of scandium and f-element complexes derived from the disiloxanediolate dianion, [(Ph2SiO)2O]2-, are reported. Reactions of in situ prepared Ln[N(SiMe3)2]3 (Ln = Eu, Sm, Gd) with (Ph2SiOH)2O in different stoichiometries afforded the lanthanide disiloxanediolates [Eu[[(Ph2SiO)2O]Li(Et2O)]3] (1), [[[(Ph2SiO)2O]Li(dme)]2SmCl(dme)] (2), and [[[((Ph2SiO)2O]Li(thf)2]2GdN(SiMe3)2] (3). In situ formed (Ph2SiOLi)2O reacted with anhydrous NdBr3 (molar ratio 3:1) to give polymeric [[Nd[(Ph2SiO)2O]3[mu-Li(thf)]2[mu2LiBrLi(thf)(Et2O)]]n] (4). Treatment of 3 with Ph2Si(OH)2 in the presence of acetonitrile yielded the dilithium trisiloxanediolate derivative [[Ph2Si(OSiPh2O)2][Li(MeCN)]2]2 (5), which according to an X-ray analysis displays an Li4O4 heterocubane structure. The trinuclear scandium complex [[[(Ph2SiO)2O]Sc(acac)2]2Sc(acac)] (6) was obtained by reaction of [(C5Me5)Sc(acac)2] (C5Me5 = eta5-pentamethylcyclopentadienyl) with (Ph2SiOH)2O in a 3:2 molar ratio. Selective formation of the colorless uranium(VI) derivative [U[Ph2Si(OSiPh20)2]2[(Ph2SiO)2O]] (7) was observed when uranocene, U(eta8-C8H8)2, was allowed to react with (Ph2SiOH)2O. An X-ray diffraction study of the solvated derivative [U[Ph2Si(OSiPh2O)2]2[(Ph2SiO)2O]].Et2O.TMEDA (TMEDA= N,N,N',N'-tetramethyl-ethylenediamine) (7a) revealed the presence of both the original [(Ph2SiO)2O]2- dianion as well as the ring-enlarged [Ph2Si(OSiPh2O)2]2- ligand in the same molecule. 相似文献
80.
Geskin VM Grozema FC Siebbeles LD Beljonne D Brédas JL Cornil J 《The journal of physical chemistry. B》2005,109(43):20237-20243
We report on a quantum-chemical study of the electronic and optical properties of unsubstituted oligo(phenylene vinylene) (OPV) radical cations. Our goal is to distinguish the impact of the choice of molecular geometry from the impact of the choice of quantum-chemical method, on the calculated optical transition energies. The geometry modifications upon ionization of the OPV chains are found to depend critically on the theoretical formalism: Hartree-Fock (HF) geometry optimizations lead to self-localization of the charged defects while pure density functional theory (DFT) results in a complete delocalization of the geometric modifications over the whole conjugated backbone. The electronic structure and vertical transition energy associated with the lowest excited state of the radical cations have been calculated at the post-Hartree-Fock level within a configuration interaction (HF-CI) scheme and using the time-dependent DFT (TD-DFT) formalism for different radical cation geometries. Interestingly, the changes in the calculated optical properties obtained when using different geometric structures are less important within a given method than the differences between methods for a given structure. The optical excitation is localized with HF-CI and delocalized with TD-DFT, almost irrespective of the molecular geometry; as a result, HF-CI excitation energies tend to saturate as the chain length increases, in contrast to the results from TD-DFT. 相似文献