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991.
Lon J. Mathias Scott Steadman Kelly Anderson Rick Davis William Jarrett Richard D. Redfearn Alan Bunn 《Macromolecular Symposia》1999,141(1):47-56
13C labeled ethylene glycol dimethacrylate (EGDMA) was used to form labeled crosslinked PMMA and model 13C labeled pendant double bond copolymers. Solution NMR was possible on solvent-swollen samples containing less than 0.5% by weight EGDMA. Spectra confirm significant amounts of singly reacted EGDMA in fully polymerized networks. Peaks arising from the two most likely stereochemical triads (syndi- and heterotactic) were identified but no evidence of cyclic species was observed. Labeled EGDMA allowed observation of the crosslink site at concentrations as low as 0.02 wt-% EGDMA. 相似文献
992.
Perinchery Narayan Marcus W Hedgcock Charles Anderson 《Magnetic resonance imaging》1993,11(8):XXXVII-XXXVIII
993.
Stephen G. Anderson Karl W. Sohlberg Stephen L. Howard Anil K. Shukla Jean H. Futrell 《Journal of the American Society for Mass Spectrometry》1991,2(6):506-510
A hemispherical energy analyzer was constructed by using a novel approach to control the fringing electrostatic field. It provides several properties useful in ion spectrometers: namely, rather simple fabrication and compact size, high transmission efficiency at moderate resolution, and the capability to adjust resolution by changing the intersphere potentials. A computer program was developed to evaluate ion trajectories through the hemispherical analyzer. Data obtained from the trajectories were used to predict the characteristics of the analyzer. Experiments performed to determine the kinetic energy dependence of the absolute transmission and the resolution functions are in accord with theoretical calculations. 相似文献
994.
K. Dadachova K. La Riviere P. Anderson 《Journal of Radioanalytical and Nuclear Chemistry》1999,240(3):935-938
Two improved processes of99Mo production have been developed on laboratory scale. The first one allows to purify Mo of natural isotopic composition from tungsten impurities from 64 to <10 ppm by using preferential adsorption of tungsten on hydrated tin(IV) oxide (SnO2 nH2O) before irradiation in a nuclear reactor. The second process deals with the separation of pure fission product99Mo from235U irradiated in a reactor. Two versions of separation process for production of fission99Mo have been developed. Both versions start with the dissolution of235U oxide target in nitric acid and are based on sequential use of alumina and anion exchange resin AG® 1-X8 columns. The yield of99Mo in both versions is 80–89%. 相似文献
995.
James A. Bresson Gordon A. Anderson James E. Bruce Richard D. Smith 《Journal of the American Society for Mass Spectrometry》1998,9(8):799-804
The simultaneous high resolution and accurate mass measurements possible with Fourier transform ion cyclotron resonance mass spectrometry coupled with the gentle ionization of electrospray hold attractions for protein, peptide, and oligonucleotide characterization, including multistage-mass spectrometry measurements for assignment of fragment masses and greater confidence in structural measurements. The detection of cyclotron motion over extended periods of time (in some cases for several minutes) allows higher resolution and mass accuracy. Generally, signal duration has been considered to be limited primarily by background pressure, with ion-neutral collisions leading to the reduction and dephasing of cyclotron motion, causing signal loss. However, recent theoretical work has shown that the ion cloud stability that is a prerequisite for high performance measurements is highly dependent on the electric field generated by the ion cloud, thus giving rise to a minimum number of charges or ions required for extended time-domain signals. The effects of ion population on ion cloud stability and signal duration, and the subsequent effects on resolution and measured isotopic abundances are reported. Individual time-domain signals for bovine insulin isotopic peaks were extracted to allow a comparison of the damping rates for each of these ion clouds and the measured time-domain amplitude maxima are shown to provide a better match with the theoretically predicted isotopic abundances for insulin. These results show that different damping rates of ions of very similar mass, but different ion cloud population sizes, can have dramatic effects on the observed isotopic patterns. Additionally, more accurate, high resolution spectra can be produced by correcting for the effects of the different damping rates that are observed for different ion population sizes. 相似文献
996.
Frankie P. Anderson John F. Gallagher Peter T. M. Kenny Clodagh Ryan David Savage 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(1):m13-m15
The title compounds, [Fe(C5H5)(C14H13O2)] and [Fe(C5H5)(C15H15O2)], respectively, contain the ferrocenyl η5(C5H4) and phenylene –C6H4– rings in a nearly coplanar arrangement, with interplanar angles of 6.88 (12) and 10.5 (2)°, respectively. Molecules of the ethyl ester form dimers through η5(C5H5)C—H⋯O=C hydrogen bonds, with graph set R(20), and, together with Csp3—H⋯π(C5H5) interactions, generate a one‐dimensional column (irregular ladder). Molecules of the isopropyl ester aggregate through η5(C5H5)C—H⋯π(C6H4) interactions. 相似文献
997.
998.
Malcolm J. Arendse Gordon K. Anderson Nigam P. Rath 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(3):237-239
In [Pt(dppe)(NO3)2], where dppe is ethylene-1,2-bis(diphenylphosphine) (C26H24P2), the Pt atom is coordinated by the two P atoms and by two O atoms of the two nitrate ions. The molecule has a distorted square-planar geometry, with one of the nitrate groups directed on each side of the plane. The cation in cis-[Pt(dppmO-O,P)2](NO3)2·2H2O, where dppmO is bis(diphenylphosphinomethyl)diphenylphosphine oxide (C25H22OP2), comprises two five-membered chelate rings, each dppmO ligand being coordinated to platinum through one P atom and the O atom. The larger P—Pt—P angle of 102.25 (4)° is due to steric interactions between the two phenyl groups on each P atom. 相似文献
999.
The sensitivity of all ion trap mass spectrometry (ITMS) methods is dependent on the trapping efficiency of the instrument. For ITMS instruments utilizing external ion sources, such as laser desorption, trapping efficiency is known to depend on the phase and amplitude of the radio frequency (RF) potential applied to the ring electrode at the time of ion introduction. It is remarkable that, in a considerable body of literature, no consensus exists regarding the effects of these parameters on the efficacy of trapping externally generated ions. In this paper, a summary of the literature is presented in order to highlight significant discrepancies. New laser desorption ion trap mass spectrometry (LD-ITMS) data are also presented, from which conclusions are drawn in our effort to clarify some of the confusion. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
1000.
Investigating chemical constraints to the measurement of phosphorus in soils using diffusive gradients in thin films (DGT) and resin methods 总被引:2,自引:0,他引:2
The effect of potential chemical constraints on the performance of two relatively new soil P testing methods, anion exchange membrane (AEM) and diffusive gradients in thin films (DGT), were evaluated. Exposures to ranges of anion (Cl(-), NO(3)(-), SO(4)(2-) and HCO(3)(-)) concentrations relevant to agricultural soils had minimal effect on P recoveries using DGT. It has also been shown previously that DGT P recoveries are unaffected by varying pH (3-9). In contrast, increasing NO(3)(-) and SO(4)(2-) concentrations in solution reduced the recovery of P using the resin method (anion exchange membrane, AEM) by 24% at 50mgL(-1) NO(3)(-) and by 47% at 12mgL(-1) SO(4)(2-) when the P concentration of the test solution was 2mgL(-1). Phosphorus sorption by the resin decreased with increasing Cl(-) concentrations until there was a 100% decrease at 300mgL(-1) Cl(-) when the P concentration of the test solution was 2mgL(-1) and a 92% reduction at 700mgL(-1) Cl(-) when the P concentration of the test solution was 0.2mgL(-1). There was also a small but significant effect of carbonate species on P sorption to the resin at carbonate concentrations that can occur in agricultural soils. Changing the pH of the solution had minimal effects on the resin P measurements in solutions above pH 4, but below pH 4, resin P measurements decreased dramatically. A poor coefficient of determination for the regression fit between DGT and resin measurements on eight agricultural soils suggested that these two methods are measuring different amounts of P for different soils. Resin P measurements increased significantly, but non-uniformly across soils, when the soil:water ratio was decreased but this did not result in an improved relationship with DGT P. There was a minimal effect on measured P using either Cl(-) or HCO(3)(-) as counter ions on the resin. 相似文献