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61.
Clark SB Turnipseed SB Nandrea GJ Madson MR Hurlbut JA Sofos JN 《Journal of AOAC International》2002,85(5):1009-1014
A confirmatory method is described for phenylbutazone (PB) residues in bovine kidney tissue. Ground kidney tissue is diluted with water, and the mixture is made basic with 25% ammonium hydroxide in water; the lipids are extracted with ethyl and petroleum ethers. The ether layer is discarded, and the tissue is acidified with 6N HCl. PB residues are extracted with tetrahydrofuranhexane (1 + 4). The extract is passed through a silica solid-phase extraction column, and the eluate is evaporated to dryness. The residue is dissolved in acidified acetonitrile-water-acetic acid (50 + 49.4 + 0.6). A single quadrupole mass spectrometer coupled to a liquid chromatograph with an electrospray interface is used to confirm the identity of the PB residues in the kidney extract. Negative-ion detection with selected-ion monitoring of 4 ions is used. Sets of control and fortified-control kidney tissues (at 50, 100, and 200 ppb PB) and several kidney tissue field samples were analyzed for method validation. The method was tested further during the course of a survey to determine the incidence of PB residues in bovine kidney samples obtained from slaughterhouses across the country. In addition, the method was tested for use with an ion-trap mass spectrometer coupled to a liquid chromatograph, which allowed confirmation of PB at lower levels (5-10 ppb) in kidney tissue. 相似文献
62.
Ruifeng Liu Paula R. Moody Alex S. Vanburen Jeffrey A. Clark Joel A. Krauser Dennis R. Tate 《Vibrational Spectroscopy》1996,10(2):325-329
Results of ab initio and density functional theory calculations on the structure and vibrational frequencies of hypophosphite anion indicate earlier experimental assignments of the fundamental vibrational modes are correct while the recent reassignments of several modes proposed by Bickley et al. are inconsistent with the calculated results. 相似文献
63.
A 14 MeV neutron activation analysis system is described that is being used primarily to determine trace levels of oxygen
in metals. No sample container is required for relatively inert solid metal samples thus increasing the sensitivity of the
method by a factor of five. Under these conditions the sensitivity and precision foroxygen is about 6±3.3 μg in a single determination,
resulting from collecting 1.216N counts per μg of oxygen. A method is described for calibrating the system for the analyses of large metal samples. The preparation
and use of sample containers for the analyses of particulate and/or reactive samples is also presented.
Work was performed at the Ames Laboratory of the U.S. Atomic Energy Commission. Contribution No. 2567. 相似文献
64.
Budarin VL Clark JH Tavener SJ Wilson K 《Chemical communications (Cambridge, England)》2004,(23):2736-2737
The reaction of localised C[double bond, length as m-dash]C bonds on the surface of activated carbons has been shown to be an effective method of chemical modification especially using microwave-assisted reactions. 相似文献
65.
The oxidation of polyethylene, polypropylene, and polystyrene by exposure to plasmas excited in pure oxygen and helium–oxygen mixtures at low power levels has been studied. A detailed curve resolution procedure is outlined, and the rate of oxidation is shown to be a strong function of the polymer structure for pure oxygen plasmas, as is the composition of the oxidized layer; this is not the case, however, for oxidation effected by helium–oxygen mixtures. It seems likely, from a consideration of the available data, that the oxidation is confined to the outermost monolayer and is initiated by a crosslinking mechanism that involves oxygen-containing functionalities. 相似文献
66.
The propagating species for 1-hexene, propene, and ethene polymerization as catalyzed by [rac-(C2H4(1-indenyl)2)Zr(CH3)][CH3B(C6F5)3] has been intercepted at T < -40 degrees C and characterized by NMR methods. Observation of the propagating species permits direct monitoring of initiation, propagation, and termination processes by NMR. Detailed examination of alkene incorporation into Zr-polymeryl species using 13C-labeled 1-alkenes supports a continuous insertion mechanism whereby the anion re-coordinates after each alkene insertion. 相似文献
67.
W. Clark Still Lawrence J. Macpherson Toshiro Harada James F. Callahan Arnold L. Rheingold 《Tetrahedron》1984,40(12):2275-2281
The conformations of macrocyclic intermediates provide a useful medium through which distant chiral centers may control chemical reactions. In this paper, we show that macrocycles made by cyclization of simple acyclic starting materials with an auxiliary spacer may be used to prepare stereochemically complex acyclic products. 相似文献
68.
trans-Pd(NO3)H(PCy3)2 (I) when treated with Et4NCl forms the hydride trans-PdClH(PCy3)2 which in turn reacts with AgPF6 in acetonitrile to give trans-[PdH(CH3CN)(PCy3)2]PF6 (III). Both I and III react smoothly with acetylenes containing one electron-withdrawing group to give alkenyl products. The geometry of the resulting alkenyl ligand implies that cis addition has occurred and that the hydridic hydrogen adds to the acetylenic carbon containing the electron-withdrawing group.Acetylenes containing two electron-withdrawing groups give mixtures from which both alkenyl and zerovalent acetylene compounds can sometimes be isolated. In the presence of proton sponge, monosubstituted acetylenes still give alkenyl products while those substituted with two electron-withdrawing groups give the zerovalent products in good yield. The relevance of these results to an understanding of the nature of the migratory insertion reaction is discussed. 相似文献
69.
H.C. Clark S.S. McBride N.C. Payne C.S. Wong 《Journal of organometallic chemistry》1979,178(2):393-408
The reaction of [Pt((F3C)CCH(CF3))(P(C2H5)3)2CH3OH]PF6 with allene in methanol affords a novel metallocyclic ethereal complex [CH3)(P(C2H5)3)2]PF6, which has been characterized by 1H, 2H, 19F and 31P NMR spectroscopy. Its structure has also been determined by a single crystal X-ray analysis. The crystal are monoclinic, space group P21/n, with cell dimensions a 20.012(5), b 17.222(5), c 8.902(3) Å and β 91.54(5)°. The structure was refined by full matrix least-squares methods on F, using 3097 unique observations collected by automated four circle diffractometer. Refinement converged at R 0.066. The Pt atom has a distorted square-planar coordination geometry, with cis P atoms, and PtP distances of 2.219(4) Å (trans to O) and 2.324(4) Å (trans to C). These results show the ethereal group is a weak ligand to platinum(II) but because of the chelating effect, its displacement by other ligands is thermodynamically not favorable. The mechanism of formation of the ethereal complex is also discussed. 相似文献
70.
S. Unsalan M. Sancar B. Bekce P. M. Clark T. Karagoz F. V. Izzettin S. Rollas 《Chromatographia》2005,61(11-12):595-598
The objective of this study was to measure plasma concentration of isoniazide (INH), pyrazinamide (PZA) and rifampisin (RIF) in tuberculosis patients by using HPLC. 100 μL of plasma was deproteinized by adding trichloroacetic acid and acetonitrile to yield INH, PZA and RIF respectively. They were analysed by HPLC using a reversed phase C18 pre-column linked to a 4 μm C18 analytical column with a gradient solvent programme, which delivered 3% to 40% (v/v) acetonitrile in phosphate buffer in 20 min at rate of 0.8 mL min?1. Signals were monitored by diode-array detector. Acetanilide was used as internal standard. The method is reproducible and accurate with lower limits of quantification of 0.6 mg L?1 for INH, 1.5 mg L?1 for PZA and 0.7 mg L?1 for RIF. The plasma of 25 patients receiving daily standard therapy were assayed for INH, PZA and RIF 3 h after administration. Plasma concentration were found between 0.98 and 6.27 mg L?1 for INH, 11.05 and 47.26 mg L?1 for PZA, 5.09 and 33.20 mg L?1 for RIF respectively. Many of the plasma levels were found to be sub therapeutic. This practical method may be used for monitoring drug plasma levels of patients who fail to respond to treatment. 相似文献