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171.
Viorica Lopez-Avila Richard Young Werner F. Beckert 《Journal of separation science》1997,20(9):487-492
This paper describes the extraction of 49 organophosphorus pesti-cides (OPPs) from water samples using solid-phase microextraction (SPME). Three fibers, including a 15-μm XAD-coated fiber, a 85-μm polyacrylate-coated fiber, and a 30-μm polydimethylsilox-ane-coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate-coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD- and polyacrylate-coated fibers. With some exceptions, the XAD- and polyacrylate-coated fibers performed better than the PDMS-coated fiber. The superiority of the XAD-nd polyacrylate-coated fiber. The superiority of the XAD- and polyacrylate-coated fibers over the PDMS-coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber. 相似文献
172.
The neutron irradiated potassium hexacyanoferrate(III) solutions were analyzed for Fe(CN)64?, Fe(CN)63?, and Prussian blue. The retention values (1.1%) were constant throughout the pH and concentration ranges studied, and did not change with the length of irradiation. The complex behavior of the radiochemical yield of the Fe(CN)64? and Prussian blue was attributed to the competition of the various reactions involved in the irradiation. 相似文献
173.
Kazufumi Takahashi Raymond N. Castle Milton L. Lee 《Journal of heterocyclic chemistry》1987,24(4):977-979
The four acridinecarbaldehydes, namely, acridine-1-carbaldehyde, acridine-2-carbaldehyde, acridine-3-carbaldehyde, and acridine-4-carbaldehyde have been synthesized for the first time. 相似文献
174.
The second-order rate constants for the nucleophilic replacement of fluorine by isopropoxide in 5,6,7,8-tetrafluoro- and 6,7,-difluoro-1,2,3,4-tetrahydro-9-alkenyl-1,4-methanonaphthalenes and related 9-alkyl systems have been measured. A factor of 6 - 7 separates the most reactive compounds [the 9- (4′-trifluoromethylbenzylidene) derivatives] from the least reactive compounds [the syn-9-isopropyl derivatives] in both the tetrafluoro- and difluoro-series. It is concluded for these small reactivity differences. 相似文献
175.
176.
J. S. Bradshaw N. W. Adams R. S. Johnson B. J. Tarbet C. M. Schregenberger M. A. Pulsipher M. B. Andrus K. E. Markides M. L. Lee 《Journal of separation science》1985,8(10):678-683
Contemporary methods for the synthesis of alkyl- and arylsubstituted polysiloxane stationary phases are reviewed. A new, moderately polar phase containing the 3-(4-methoxyphenyl)-propyl group is reported. 相似文献
177.
Dinuclear iron(II)-cyanocarbonyl complex [PPN](2)[Fe(CN)(2)(CO)(2)(mu-SEt)](2) (1) was prepared by the reaction of [PPN][FeBr(CN)(2)(CO)(3)] and [Na][SEt] in THF at ambient temperature. Reaction of complex 1 with [PPN][SEt] produced the triply thiolate-bridged dinuclear Fe(II) complex [PPN][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)] (2) with the torsion angle of two CN(-) groups (C(5)N(2) and C(3)N(1)) being 126.9 degrees. The extrusion of two sigma-donor CN(-) ligands from Fe(II)Fe(II) centers of complex 1 as a result of the reaction of complex 1 and [PPN][SEt] reflects the electron-rich character of the dinuclear iron(II) when ligated by the third bridging ethylthiolate. The Fe-S distances (2.338(2) and 2.320(3) A for complexes 1 and 2, respectively) do not change significantly, but the Fe(II)-Fe(II) distance contracts from 3.505 A in complex 1 to 3.073 A in complex 2. The considerably longer Fe(II)-Fe(II) distance of 3.073 A in complex 2, compared to the reported Fe-Fe distances of 2.6/2.62 A in DdHase and CpHase, was attributed to the presence of the third bridging ethylthiolate, instead of pi-accepting CO-bridged ligand as observed in [Fe] hydrogenases. Additionally, in a compound of unusual composition ([Na.(5)/(2)H(2)O][(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)])(n)((1)/(2)O(Et)(2))(n) (3), the Na(+) cations and H(2)O molecules combining with dinuclear [(CN)(CO)(2)Fe(mu-SEt)(3)Fe(CO)(2)(CN)](-) anions create a polymeric framework wherein two CN(-) ligands are coordinated via CN(-)-Na(+)/CN(-)-(Na(+))(2) linkages, respectively. 相似文献
178.
Price WJ Kuo PK Lee TR Colorado R Ying ZC Liu GY 《Langmuir : the ACS journal of surfaces and colloids》2005,21(18):8422-8428
Nanostructures of self-assembled monolayers (SAMs) are designed and produced using coadsorption and nanografting techniques. Because the structures of these artificially engineered domains are predesigned and well-characterized, a systematic investigation is possible to study the mechanical responses to force modulation under atomic force microscope tips. Force modulation imaging reveals characteristic contrast sensitivity to changes in molecular-level packing, molecule chain lengths, domain boundaries, and surface chemical functionalities in SAMs. By means of actively tuning the driving frequency, the resonances at the tip-surface contact are selectively activated. Therefore, specific surface features, such as the edges of the domains and nanostructures or desired chemical functionalities, can be selectively enhanced in the amplitude images. These observations provide a new and active approach in materials characterization and the study of nanotribology using atomic force microscopy. 相似文献
179.
Tae Oan Ahn Jung Ho Kim Jong Chan Lee Han Mo Jeong Jong-Yoon Park 《Journal of polymer science. Part A, Polymer chemistry》1993,31(2):435-441
A macro-azoinitiator containing polyarylate segment and azo group was prepared by the solution polycondensation of azobiscyanopentanoyl chloride and hydroxy-terminated polyarylates having viscosity-average molecular weights of 6200, 8100, and 12 400. These macro-azoinitiators were used in the radical polymerization of styrene to synthesize polyarylate-polystyrene block copolymers. Thermal properties measured by the differential scanning calorimetry indicated the phase separated morphology of the block copolymers except at low molecular weight of the block constituents. © 1993 John Wiley & Sons, Inc. 相似文献
180.
Ovshinsky SR Young RT Allred DD DeMaggio G Van der Leeden GA 《Physical review letters》1987,58(24):2579-2581