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The use of membrane tubing for the introduction of reagents for the determination of phosphate in waters by flow injection analysis was studied. The use of membranes eliminates the need for confluence points in the design of flow injection manifolds. This increases the sensitivity of the manifold by providing a sufficient reagent excess for the reaction without diluting the sample. Methods for the introduction of acid, molybdate and hydrazine were devised for the determination of phosphate by the Molybdenum Blue method. Several membranes were examined and Nafion and Accurel (microporous polypropylene) were found to be most useful. Molybdate introduction was achieved using a supported liquid membrane (SLM). Calibration was linear and a detection limit of 12 ppb phosphate (4 ppb phosphorus) was obtained. 相似文献
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Alan J. Chalk 《Journal of organometallic chemistry》1974,76(2):C38-C39
Reactions of MI(CH3)(PPh3)2 or MCl(CH2COR)(PPh3)2 (M = Pd, Pt) with sodium dicyanomethanide in methanol gave novel metal complexes. Spectroscopic data suggest that these complexes contain either an iminoether chelate ring or a carbon-carbon chelate ring which was derived from CH(CN)2-. 相似文献
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A 1H MRS study of probable Alzheimer's disease and normal aging: implications for longitudinal monitoring of dementia progression 总被引:10,自引:0,他引:10
Rose SE de Zubicaray GI Wang D Galloway GJ Chalk JB Eagle SC Semple J Doddrell DM 《Magnetic resonance imaging》1999,17(2):291-299
In order to evaluate the capability of 1H MRS to monitor longitudinal changes in subjects with probable Alzheimer's disease (AD), the temporal stability of the metabolite measures N-acetylaspartate and N-acetylaspartylglutamate (NA), total Creatine (Cr), myo-Inositol (mI), total Choline (Chol), NA/Cr, mI/Cr, Chol/Cr and NA/mI were investigated in a cohort of normal older adults. Only the metabolite measures NA, mI, Cr, NA/Cr, mI/Cr, and NA/mI were found to be stable after a mean interval of 260 days. Relative and absolute metabolite measures from a cohort of patients with probable AD were subsequently compared with data from a sample of normal older adult control subjects, and correlated with mental status and the degree of atrophy in the localized voxel. Concentrations of NA, NA/Cr, and NA/mI were significantly reduced in the AD group with concomitant significant increases in mI and mI/Cr. There were no differences between the two groups in measures of Cr, Chol, or Chol/Cr. Significant correlations between mental status as measured by the Mini-Mental State Examination and NA/mI, mI/Cr and NA were found. These metabolite measures were also significantly correlated with the extent of atrophy (as measured by CSF and GM composition) in the spectroscopy voxel. 相似文献
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Caio T. Inácio Alberto M. T. Magalhães Paulo O. Souza Phillip M. Chalk Segundo Urquiaga 《Isotopes in environmental and health studies》2018,54(2):185-195
Variations in the relative isotopic abundance of C and N (δ13C and δ15N) were measured during the composting of different agricultural wastes using bench-scale bioreactors. Different mixtures of agricultural wastes (horse bedding manure?+?legume residues; dairy manure?+?jatropha mill cake; dairy manure?+?sugarcane residues; dairy manure alone) were used for aerobic–thermophilic composting. No significant differences were found between the δ13C values of the feedstock and the final compost, except for dairy manure?+?sugarcane residues (from initial ratio of ?13.6?±?0.2?‰ to final ratio of ?14.4?±?0.2?‰). δ15N values increased significantly in composts of horse bedding manure?+?legumes residues (from initial ratio of +5.9?±?0.1?‰ to final ratio of +8.2?±?0.5?‰) and dairy manure?+?jatropha mill cake (from initial ratio of +9.5?±?0.2?‰ to final ratio of +12.8?±?0.7?‰) and was related to the total N loss (mass balance). δ13C can be used to differentiate composts from different feedstock (e.g. C3 or C4 sources). The quantitative relationship between N loss and δ15N variation should be determined. 相似文献
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The purity of methyl nitrite prepared by the esterification of methanol with aqueous nitrous acid was determined by absorbing gaseous samples in solutions of acidic potassium permanganate and hydriodic acid. Nitrate formed in the oxidation reaction was determined by steam distillation, and iodomethane formed in hydriodic acid was determined by gas-liquid chromatography. The method was used to evaluate purification procedures. 相似文献
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A. J. Chalk T. J. Hoogeboom 《Journal of polymer science. Part A, Polymer chemistry》1969,7(9):2537-2545
Lithiated poly(2,6-dimethyl-1,4-phenylene ether) has been used as an initiator for the graft polymerization of isoprene, methyl methacrylate, hexamethylcyclotrisiloxane, and phenyl isocyanate with the use of toluene and tetrahydrofuran as solvents. The products were examined by gel-permeation chromatography for evidence of homopolymerization and graft polymerization. The composition of the graft copolymers was determined by NMR, and for isoprene and hexamethylcyclotrisiloxane, termination by trialkylchlorosilanes enabled chain lengths to be determined by NMR. The use of toluene gave rise to some homopolymerization, but with tetrahydrofuran, only hexamethylcyclotrisiloxane gave homopolymer. In all cases, graft copolymers were formed. With isoprene and methyl methacrylate, soluble graft copolymers were formed in good yield. In the former case approximately 60% 3,4 and 40% 1,4 addition was found. In the latter case 1,1-diphenylethylene was used to reduce crosslinking, in its absence, methyl methacrylate gave only crosslinked gels in tetrahydrofuran. Hexamethylcyclotrisiloxane added only one molecule per lithium on the polymer, the remainder giving homopolymer. Phenyl isocyanate gave some soluble graft copolymer in toluene, but only crosslinked products were obtained when tetrahydrofuran was used as reaction solvent. 相似文献
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An apparatus and procedure are described for preparing nitrogen gas samples for precise 13N: 14N measurement. Gas is generated by reaction of ammonium sulphate with alkaline hypobromite in an evacuated system. The design of the apparatus and its recommended mode of operation overcome the problem of air contamination of samples. The gas is cleaned by liquid nitrogen freezing and is transferred to a sample tube with a Toepler pump, so that it can be analysed quickly and conveniently on a mass spectrometer. 相似文献
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