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991.
A method is described for the precise determination of carbon and hydrogen in milligram, amounts of sample. The method is based on the manometric measurement of the amounts of carbon dioxide and water formed on combustion. A precision mercury manometer is used in which pressures are converted to mercury volumes. The latter are measured with the aid of a commercial piston-type buret using a photo-electric level indication. 相似文献
992.
Simultaneous determination of cefazolin in rat blood and brain by microdialysis and microbore liquid chromatography 总被引:3,自引:0,他引:3
A sensitive microbore liquid chromatographic method combined with the minimally invasive technique of microdialysis was devised for simultaneously and continuously monitoring the levels of unbound blood and brain cefazolin in rats. Microdialysis probes were inserted into the jugular vein and brain striatum for blood and brain sampling, respectively. Chromatographic conditions consisted of a mobile phase of methanol-acetonitrile-100 mM monosodium phosphoric acid (20:10:70, v/v, pH 4.5) pumped through a microbore reversed-phase column at a flow rate of 0.05 mL/min. The ultraviolet detection wavelength was set at 270 nm. An on-line design allowed direct and continuous analysis of protein-free samples in the dialysate. Microdialysis probes, being home-made, were screened for acceptable in vivo recovery. Chromatographic resolution and detection were validated for response linearity as well as intra-day and inter-day variabilities. This method was then applied to pharmacokinetic profiling of protein unbound cefazolin in both the blood and brain following intravenous administration (10 mg/kg, i.v., n = 6). Rapid appearance of cefazolin in the rat brain striatal dialysate following drug injection suggested good blood-brain barrier penetration. According to a non-compartmental pharmacokinetics model, the area under the concentration (AUC) vs time ratio of cefazolin in rat brain and blood was 6%. 相似文献
993.
Protein profiling of rat cerebella during development 总被引:7,自引:0,他引:7
Protein profiles of developing rat cerebella were analyzed by means of two-dimensional gel electrophoresis (2-DE) and mass spectrometry (MS). The analysis of adult rat cerebellum gave rise to a protein map comprising approximately 3000 spots detectable by silver staining following high resolution 2-DE with a pH range of 3-10 and a mass range of 8-100 kDa. To obtain landmarks for comparison of developmental profiles of cerebellar proteins, 100 spots were subjected to peptide mass fingerprinting using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS), and 67 spots were assigned on the map. Analysis of profiles of the developing cerebella revealed significant changes in the expression of proteins during development. In most cases the expression levels of proteins increased as the cerebellum matured, while the expression of 42 spots appeared specific or remarkably abundant in the immature cerebellum. Peptide mass fingerprinting of these spots allowed us to identify 29 proteins, which include, in addition to proteins of unknown function, many proteins known to have roles in the development of the central nervous system. These results suggest that the proteomic approach is valuable for mass identification of proteins involved in cerebellar morphogenesis. 相似文献
994.
C.L. Liu X.Y. Wang Z.M. Wang S.S. Li C.T. Xin H.F. Wang B. Li L. Jiang 《Journal of Radioanalytical and Nuclear Chemistry》2001,250(3):587-591
The migration of 99Tc in a weak loess aquifer was investigated in-situ with undisturbed aquifer medium columns. The columns were obtained horizontally at a depth of 3236 m in an Underground Research Facility (URF). Quartz containing 3H (HTO) and 99Tc (in the form of 99TcO4
-) was introduced into one end of the columns and the columns were covered tightly. Aquifer water was introduced into the columns directly from an experimental shaft in the UFR. Effluents from the columns were collected and the activity of 3H and 99Tc were determined with a liquid scintillation analyzer. The breakthrough curves of 3H and 99Tc indicate that 99Tc migrates a little faster than that 3H does in the aquifer. 相似文献
995.
The velocity imaging photoionisation coincidence (VIPCO) technique is shown to be a powerful tool for studies of ion pair formation. Sequential mechanisms are demonstrated for some three-body ion pair formation reactions. Observation of a new type of reaction producing one negatively and two positively charged ions plus an electron is reported. 相似文献
996.
G. H. Gelinck J. M. Warman H. F. M. Schoo 《Journal of Radioanalytical and Nuclear Chemistry》1998,232(1-2):115-120
Using the pulse-radiolysis time-resolved microwave conductivity technique the mobility and decay kinetics of radiation-induced
charge carriers is studied in a series of poly(2,5-dialkoxy-phenylene vinylene) derivatives. The lower limit to the sum of
the mobilities of the positive and negative charge carriers, Σμmin, depends strongly on the alkoxy functionalization and ranges from 1.2·10−7 to 1.4·10−6 m2/V·s at room temperature. Σμmin increases with the degree of order in the material. The after-pulse conductivity decay kinetics are disperse and are controlled
by a combination of charge recombination and trapping. 相似文献
997.
Jiang J Renshaw JC Sarsfield MJ Livens FR Collison D Charnock JM Eccles H 《Inorganic chemistry》2003,42(4):1233-1240
The solution chemistry of uranyl ion with iminodiacetate (IDA) and oxydiacetate (ODA) was investigated using NMR and EXAFS spectroscopies, potentiometry, and calorimetry. From the NMR and EXAFS data and depending on stoichiometry and pH, three types of metal:ligand complex were identified in solution in the pH range 3-7: 1:1 and 1:2 monomers; a 2:2 dimer. From NMR and EXAFS data for the IDA system and previous studies, we propose the three complex types are [UO(2)(IDA)(H(2)O)(2)], [UO(2)(IDA)(2)](2)(-), and [(UO(2))(2)(IDA)(2)(mu-OH)(2)](2)(-). From EXAFS spectroscopy, similar 1:1, 2:2, and 1:2 complexes are found for the ODA system, although (13)C NMR spectroscopy was not a useful probe in this system. For the 1:1 and 1:2 complexes in solution, EXAFS spectroscopy is ambiguous because the data can be fitted with either a long U-N/O(ether) value (ca. 2.9 A) suggesting 1,7-coordination of the ligand or a U-C interaction at a similar distance, consistent with terminal bidentate coordination. However, the NMR data of the IDA system suggest that 1,7-coordination is the more likely. The stability constants of the three complexes were determined by potentiometric titrations; the log beta values are 9.90 +/-, 16.42 +/-, and 10.80 +/- for the 1:1, 1:2, and 2:2 uranyl-IDA complexes, respectively, and 5.77 +/-, 7.84 +/-, and 4.29 +/- for the 1:1, 1:2, and 2:2 uranyl-ODA complexes, respectively. The thermodynamic constants for the complexes were calculated from calorimetric titrations; the enthalpy changes (kJ mol(-)(1)) and entropy changes (J K(-)(1) mol(-)(1)) of complexation for the 1:1, 1:2, and 2:2 complexes respectively are the following. IDA: 12 +/- 2, 230 +/- 8; 8 +/- 2, 151 +/- 9; -33 +/- 3, -283 +/- 11. ODA: 26 +/- 2, 198 +/- 12; 20 +/- 2, 106 +/- 8; -24 +/- 2; -219 +/- 8. 相似文献
998.
Magnetization and electronic Raman data are presented for salts of the type Cs[Ga:Ti](SO(4))(2) x 12H(2)O, which enable a very precise definition of the electronic structure of the [Ti(OH(2))(6)](3+) cation. The magnetization data exhibit a spectacular deviation from Brillouin behavior, with the magnetic moment highly dependent on the strength of the applied field at a given ratio of B/T. This arises from unprecedented higher-order contributions to the magnetization, and these measurements afford the determination of the ground-state Zeeman coefficients to third-order. The anomalous magnetic behavior is a manifestation of Jahn-Teller coupling, giving rise to low-lying vibronic states, which mix into the ground state through the magnetic field. Electronic Raman measurements of the 1%-titanium(III)-doped sample identify the first vibronic excitation at approximately 18 cm(-1), which betokens a substantial quenching of spin-orbit coupling by the vibronic interaction. The ground-state Zeeman coefficients are strongly dependent on the concentration of titanium(III) in the crystals, and this can be modeled as a function of one parameter, representing the degree of strain induced by the cooperative Jahn-Teller effect. This study clearly demonstrates the importance that the Jahn-Teller effect can have in governing the magnetic properties of transition metal complexes with orbital triplet ground terms. 相似文献
999.
P. Quevauviller M. Lachica E. Barahona A. Gomez G. Rauret A. Ure H. Muntau 《Fresenius' Journal of Analytical Chemistry》1998,360(5):505-511
Single extraction tests are commonly used to study the eco-toxicity and mobility of metals in soils, e.g. to assess the bioavailable
metal fraction (and thus to estimate the related phyto-toxic and nutritional deficiency effects) and the environmentally accessible
trace metals upon disposal of e.g. sediment on to a soil (e.g. contamination of ground waters). However, the lack of uniformity
in the different procedures does not allow the results to be compared worldwide nor the procedures to be validated. This paper
describes the interlaboratory testing of EDTA- and DTPA-extraction procedures for soil analysis, followed by the preparation
of a calcareous soil reference material (CRM 600), the homogeneity and stability studies and the analytical work performed
for the certification of the EDTA- and DTPA- extractable contents of some trace metals (following the standardized extraction
procedures).
Received: 21 May 1997 / Revised: 4 July 1997 / Accepted: 9 July 1997 相似文献
1000.
The elemental quantification in plasma-based SNMS is hampered by the matrix dependence of the detection efficiencies. The signals of elements of unknown compounds can only be converted to concentrations with mean detection factors resulting in concentrations with an uncertainty mainly given by the matrix effect. This situation can be considerably improved by energy measurements of the sputtered particles. The energy distribution (ED) can be used in two ways. First, the exact knowledge of the ED to each detected element allows an element specific integration of the directly sputtered atoms eliminating thermal species from resputtered wall deposition. For a set of copper compounds the spread of the Cu detection factors could be reduced from ± 63% for the conventional measurement to ± 35% using energy resolved data. Second, the shape of the ED of postionised atoms differs considerably from all interfering species, such as clusters as well as twice charged atoms which could superimpose on the atomic signals. A quantitative shape analysis of the measured ED was developed to correct for these interfering species. Examples are given for both superpositions with cluster intensities and interferences with twice charged intensities. To reduce the additional time necessary to obtain the ED, the number of energy resolved data points was reduced in steps down to 3 points only which still reduced a superposition error to half of the value without ED based correction. 相似文献