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931.
Michaud AL Frank AJ Ding C Zhao X Douglas DJ 《Journal of the American Society for Mass Spectrometry》2005,16(6):835-849
Modeling of ion motion and experimental investigations of ion excitation in a linear quadrupole trap with a 4% added octopole field are described. The results are compared with those obtained with a conventional round rod set. Motion in the effective potential of the rod set can explain many of the observed phenomena. The frequencies of ion oscillation in the x and y directions shift with amplitude in opposite directions as the amplitudes of oscillation increase. Excitation profiles for ion fragmentation become asymmetric and in some cases show bistable behavior where the amplitude of oscillation suddenly jumps between high and low values with very small changes in excitation frequency. Experiments show these effects. Ions are injected into a linear trap, stored, isolated, excited for MS/MS, and then mass analyzed in a time-of-flight mass analyzer. Frequency shifts between the x and y motions are observed, and in some cases asymmetric excitation profiles and bistable behavior are observed. Higher MS/MS efficiencies are expected when an octopole field is added. MS/MS efficiencies (N(2) collision gas) have been measured for a conventional quadrupole rod set and a linear ion trap with a 4% added octopole field. Efficiencies are chemical compound dependent, but when an octopole field is added, efficiencies can be substantially higher than with a conventional rod set, particularly at pressures of 1.4 x 10(-4) torr or less. 相似文献
932.
Push-pull 2-alkylidene-4-oxothiazolidine vinyl bromides undergo efficient C(5) functionalization through DMSO-assisted carbon-bromine cleavage, followed by a bromine transfer-substitution (or elimination) sequence. A mechanism for this novel transformation is proposed. 相似文献
933.
Electrically conducting poly(3,4‐ethylenedioxythiophene) (PEDOT) film doped with silicomolybdate (SiMo12O404? or SiMo12) was synthesized by electrochemical polymerization. The synthesized film is capable of fast charge propagation during redox reactions in strong acid medium 0.2 M H2SO4 solution. The modified electrode was used towards reduction of bromate and successfully employed as an amperometric sensor for bromate and also above modified electrode was investigated for ascorbic acid oxidation. 相似文献
934.
An efficient and a quick microwave‐assisted synthesis of benzimidazoles and trisubstituted imidazoles was developed. Three benzimidazoles were obtained as a result of the condensation of 1,2‐phenylenediamine with carboxylic acids and acetoacetic ester without catalyst. A series of trisubstituted imidazoles were synthesized by condensation of benzil, aromatic aldehyde and ammonium acetate in the presence of glacial acetic acid. 相似文献
935.
Zeisler R 《Analytical and bioanalytical chemistry》2004,378(5):1277-1283
NIST maintains a portfolio of more than 1300 standard reference materials (SRM), more than a third of these relating to measurements in the biological and environmental fields. As part of the continuous renewal and replacement efforts, a set of new marine sediments has been recently developed covering organic and inorganic determinations. This paper describes the steps taken in sample preparation, homogeneity assay, and analytical characterization and certification with specific emphasis on SRM 2702 inorganics in marine sediment. Neutron activation analysis showed the SRM to be highly homogeneous, opening the possibility for use with solid sampling techniques. The certificate provides certified mass fraction values for 25 elements, reference values for eight elements, and information values for 11 elements, covering most of the priority pollutants with small uncertainties of only several percent relative. The values were obtained by combining results from different laboratories and techniques using a Bayesian statistical model. An intercomparison carried out in field laboratories with the material before certification illustrates a high commutability of this SRM.Electronic Supplementary Material Supplementary material is available in the online version of this article at 相似文献
936.
Dipl.-Ing. Dr. O. Hinterhofer 《Monatshefte für Chemie / Chemical Monthly》1974,105(2):279-290
The selective chlorination of a m/p-xylene mixture, followed by distillation of the unreacted p-xylene, leaves a residue containing up to 90% of monochlorinated m-xylenes. m-Xylene is recovered from the latter by heterogeneous catalytic hydrogenolysis in the gas-phase. It was found that the hydrogenolysis on certain noble metal catalysts proceeds according to an ionic reaction mechanism at temperatures below a definite temperature range. At temperatures above this range hydrogenolysis follows a radical reaction mechanism. 相似文献
937.
Ken Ohwada 《Polyhedron》1984,3(7):853-859
From the analysis of the electrostatic potential near the core-valence boundary in an atom, it is shown that the Pauling electronegativity scale χp is approximately given by the formula, where Nv is the valence electron number and f(n) is some function of the periodic number in the periodic table. It is also shown in detail that the Pauling electronegativity scale is closely related to the Wang-Parr electronegativity scale which is determined as the negative of the chemical potential in density functional theory. Correlation between the Pauling and Mulliken electronegativities is briefly discussed. 相似文献
938.
W. Schr?n A. Detcheva B. Dre?ler K. Danzer 《Fresenius' Journal of Analytical Chemistry》1998,361(2):106-109
Direct solid sampling graphite furnace AAS (SS-GF-AAS) provides an advantageous alternative to the conventional AAS which
requires wet digestion of the samples. This method is suitable for trace element determination in calcium fluoride and other
fluoride-containing samples. Matrix effects were studied by using calibration standards, certified reference materials with
different matrices and by means of three-dimensional calibration. 3D calibration is suitable for selection of calibration
samples for more reliable analyses. Cu, Pb, Cd, Zn, and Fe were determined by means of calibration with variation of sample
weight using certified reference materials and suitable fluoride-containing calibration samples.
Received: 25 July 1997 / Revised: 15 December 1997 / Accepted: 20 December 1997 相似文献
939.
Jo‐Nan Chen Fang‐Ming Hsu Hui‐Chun Wang Chung‐Wen Wu Pao‐Swu Cheng Wen‐Liang Tsai 《中国化学会会志》2006,53(4):931-938
Four series of compounds 11?50 containing terminal alicyclic rings such as cyclohexylmethyl, cyclopentylmethyl, cyclobutylmethyl, and cyclopropylmethyl rings were synthesized and their liquid crystal behavior studied. The ring size and the length of flexible alkoxy chain influence the phase formation in different ways. While the smaller ring and the shorter alkoxy chain tend to favor the formation of the N phase, the larger ring and the longer alkoxy chain tend to favor the formation of the SmC phase. All the compounds except 11 and 21 exhibit SmA phases. The widest temperature range of the N, SmA, and SmC phases are found in the compounds 41 , 46 , and 20 , respectively, which are 75 °C for 41 , 115 °C for 46 , and 100 °C for 20 . 相似文献
940.
Fernando Mendizabal Dana Reyes Claudio Olea‐Azar 《International journal of quantum chemistry》2006,106(4):906-912
Hydrogen bonding and metallophilic attractions are studied in the model systems: [(AuNH3Cl)2], [(AuNH(CH3)2Cl)2], [{Au2(μ‐SH)(PH2O)(PH2OH)}2], [(CuNH3Cl)2], and [{Cu(NH3)Cl}4] at the Hartree–Fock (HF) and second‐order Møller–Plesset (MP2) levels. The two interactions are found to be comparable and prevailing in the final structure. It is determined that the aurophilic contact has a same magnitude that the hydrogen bonding, and is stronger than the cuprophilic interaction. The presence of hydrogen bond directs the growth of the crystal. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献