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11.
Isotope dilution is a useful technique to measure the labile metal pool, which is the amount of metal in soil in rapid equilibrium (<7 days) with the soil solution. This is normally performed by equilibrating soil with a metal isotope, and sampling the labile metal pool by using an extraction (E value), or by growing plants (L value). For Cu, this procedure is problematic for E values, and impossible for L values, due to the short half-life of the 64Cu radioisotope (12.4 h), which makes access and handling very difficult. We therefore developed a technique using enriched 65Cu stable isotope and measurement of 63Cu/65Cu ratios by quadrupole inductively coupled plasma mass spectrometry (ICP-MS) to measure labile pools of Cu in soils using E value techniques. Mass spectral interferences in detection of 63Cu/65Cu ratios in soil extracts were found to be minimal. Isotope ratios determined by quadrupole ICP-MS compared well to those determined by high-resolution (magnetic sector) ICP-MS. E values determined using the stable isotope technique compared well to those determined using the radioisotope for both uncontaminated and Cu-contaminated soils.  相似文献   
12.
A sensitive LC-MS-MS method for the direct determination and quantification of 15 fluorobenzoic acids (FBAs) was developed. FBAs are used as conservative tracers for hydrological modelling of water flow and in studies of pesticides and other xenobiotic compounds. The use of FBAs is discussed in relation to other tracers (bromide, chloride, uranine). The method covers mono-substituted fluorobenzoic acid, difluorobenzoic acid, trifluorobenzoic acid, and tetrafluorobenzoic acid. The general detection limit in ground water was 1 microg/l using electrospray ionisation and 20 microg/l using atmospheric pressure chemical ionisation. Analysis time was less than 10 min, small sample volumes were needed and no clean-up was required.  相似文献   
13.
A systematic study was conducted on the Cr catalysed tri- and tetramerisation of ethylene using bis(diphenylphosphino)amine ligands with N-aryl functionality. This study revealed that the oligomerisation reaction product selectivity is primarily dependent on the structure and size of the N-aryl groups.

Addition of sufficient steric bulk to the N-phenyl group via ortho-alkyl substitution increased the combined 1-hexene and 1-octene selectivity (overall alpha selectivity) to above 82% at an overall 1-octene selectivity of 56%. The introduction of a single carbon spacer between the N-atom and the aryl-moiety, as well as the addition of branching on this carbon, resulted in further selectivity improvements, achieving an overall 1-octene selectivity of 64% and an overall alpha selectivity of 84%. This was obtained at catalyst productivities in excess of 1,000,000 g/g Cr/h.  相似文献   

14.
Intermediates with π-bonded Si or Ge are generated during gas phase pyrolysis of 1,2-disila- or 1,2-digerma-cyclohex-4-enes.Compounds such as R2MMR2 are successfully trapped by addition or [2 + 2] and [4 + 2] cycloadditions. These results were proved by mass spectrometry.  相似文献   
15.
Crystalline salts of the hydrolytic dimer of Cr(III), [Cr2(μ-OH)2(H2O)8]X4·n H2O (X = p-toluenesulfonate (tos) or mesitylene-2-sulfonate (dmtos)) have been prepared in good yields via a simple two-step procedure: H+ oxidation of Cr metal to give Cr2+ (T ≈? 70°) followed by O2 oxidation, of Cr2+ to give the dimer (T ≈? 25°). The mechanism of conversion of Cr2+ into the dimer is discussed.  相似文献   
16.
The construction of immunochemical inhibition assays for beta-agonist and hormone residues have previously been described. In the present work the beta-agonist assay was further optimised for application to biological samples, using urine as the main model matrix. Matrix interferences with the antigen-antibody interaction and non-specific binding (NSB) of matrix components to the sensor surface were systematically studied. A full factorial design experiment was employed for evaluating the effects of assay buffer composition. In addition, the influence of antibody concentration and sample dilution on the matrix background was investigated. NSB from urine was highly affected by buffer pH and salt concentration, while buffer composition had little effect on matrix interferences with the antigen-antibody interaction. Ultra-filtration efficiently prevented NSB from urine and serum samples. Increased antibody dilution reduced the matrix background while sample dilution had an opposite effect.  相似文献   
17.
Coordinative Anchoring of Nickel Complexes on Hectorite-Layer Silicates through long-chain Diphenylphosphine Groups The treatment of sodium and calcium hectorites with 2-diphenylphosphinoethyltriethoxysilane leads, by condensation of free hydroxyl groups, to functionalized layer silicates with long-chain diphenylphosphine groups onto which nickel chloride can be coordinated. In these modified hectorites the fourth coordination site of the tetrahedrally coordinated nickel is occupied by a labile solvent molecule. On the other hand, the complex bis(2-diphenylphosphinoethyltriethoxysilane)nickel(II) chloride prepared beforehand also reacts with sodium hectorite under condensation; but the square-planar coordination of the four stable ligands (two chloride and two phosphor atoms) is maintained. This finds its expression in a significant activity decrease in catalytic reactions as compared to the aforementioned products.  相似文献   
18.
19.
A technique for the separation and preconcentration of Cr(VI) and Cr(III) in fresh waters is presented. The analytical procedure involves the use of anion- and cation-exchange columns. The columns are eluted and the eluate is analysed for chromium using a graphite furnace atomic absorption spectrometer. The recovery of Cr(VI) and Cr(III) is 97.86 ± 1.31% and 102.36 ± 1.25% (95% confidence), respectively. The detection limits are 0.019 and 0.020 μg 1?1 for 200 ml of sample (twice the standard deviation of eleven replicate blanks). The method is rapid and the need for minimum sample handling avoids contamination problems.  相似文献   
20.
Mechanistic investigations of the ethylene tetramerisation reaction   总被引:8,自引:0,他引:8  
The unprecedented selective tetramerisation of ethylene to 1-octene was recently reported. In the present study various mechanistic aspects of this novel transformation were investigated. The unusually high 1-octene selectivity in chromium-catalyzed ethylene tetramerisation reactions is caused by the unique extended metallacyclic mechanism in operation. Both 1-octene and higher 1-alkenes are formed by further ethylene insertion into a metallacycloheptane intermediate, whereas 1-hexene is formed by elimination from this species as in other reported trimerisation reactions. This is supported by deuterium labeling studies, analysis of the molar distribution of 1-alkene products, and identification of secondary co-oligomerization reaction products. In addition, the formation of two C6 cyclic products, methylenecyclopentane and methylcyclopentane, is discussed, and a bimetallic disproportionation mechanism to account for the available data is proposed.  相似文献   
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