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81.
82.
Andrzej Rykowski Eliza Guzik Mieczyslaw Makosza Wolfgang Holzer 《Journal of heterocyclic chemistry》1993,30(2):413-418
The configuration of (3-substituted)-1,2,4-triazin-5-ylcarbaldoximes and (3-substituted)alkyl-1,2,4-triazin-5-ylketoximes was determined by means of 1H-nmr, 13C-nmr, 15N-nmr and homonuclear NOE-difference spec-troscopy. Oximes resulting from reaction of 1,2,4-triazines with nitroalkanes were found to be either pure E-isomers or E/Z-mixtures with the amount of E-isomer greatly predominating. Detailed 13C-nmr data of the oximes investigated are presented. 相似文献
83.
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86.
The voltammetric method of Cr(VI) determination in a flow system is proposed. Determinations can be carried out in the simultaneous presence of an excess of Cr(III), complexing agents, humic substances and surfactants. The method is based on the combination of a selective accumulation of the product of Cr(VI) reduction to the metallic state and a very sensitive voltammetric method of chromium determination in the presence of DTPA and nitrates. The calibration graph is linear from 1×10?9 to 5×10?8 mol L?1 for accumulation time of 30 s. The relative standard deviation is 5.2% (n=5) for Cr(VI) concentration 1×10?8 mol L?1. The influence of humic and fulvic acids, complexing agents and surfactants on Cr(VI) and the interfering Cr(III) signal is presented. The method was applied to Cr(VI) determination in certified reference material, soil sample, natural water sample and EDTA extracts from soil certified reference material. 相似文献
87.
A selective and sensitive method for determination of traces of Cr(VI) in the presence of a large excess of Cr(III) by differential pulse catalytic adsorptive stripping voltammetry is presented. For minimization of Cr(III) interference nitrilotriacetic acid was used as a masking agent. The determinations were performed in a flow system. The calibration plot was linear from 1×10−10 to 1×10−8 mol L−1 for accumulation time 60 s. The relative standard deviation for 3×10−9 mol L−1 Cr(VI) was 4.1% (n=5). The detection limit for an accumulation time of 60 s was 4×10−11 mol L−1. The influence of common foreign ions is also presented. The performance of the method was verified by analysis of certified reference material for Cr(VI) and comparing the results of analyses of natural water samples with those obtained by another accepted electrochemical method. 相似文献
88.
M. Lapkowski K. Waskiewicz R. Gabanski J. Zak J. Suwiński 《Russian Journal of Electrochemistry》2006,42(12):1267-1274
Four new compounds: 1,4-dimetoxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene), 1,4-dietoxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene),
1,4-isopropyloxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene) and 1,4-dietoksy-2,5-bis[2-(5-methylthiophen-2-yl)ethenyl]benzene are
synthesized. Three steroisomers ZZ, EZ and EE are isolated from the reaction mixture for the first two of them. Third compound
is fully converted to the most stable EE form. Polymerization of all isomers leads to identical polymeric product. Mechanism
of polymerization is recognized by using model molecule with methyl substituents blocking α-, α′-sites. All seven stereoisomers
have photoluminescent properties. Detailed spectral and electrochemical studies reveal isomerization phenomena during oxidation
or at light exposure.
Published in Russian in Elektrekhimiya, 2006, Vol. 42, No. 12, pp. 1401–1408.
Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes.” October 18–22,
2005, Moscow.
The text was submitted by the authors in English. 相似文献
89.
A procedure for trace thallium determination by anodic stripping voltammetry at a bismuth film electrode is presented. Measurements were performed in a flow system. The calibration graph was linear from 2×10?9 to 3×10?8 mol L?1 for an accumulation time of 300 s. A detection limit for Tl+ following deposition time of 300 s was 6×10?10 mol L?1. The relative standard deviation at Tl+ concentration 2×10?8 mol L?1 was 3.9%. For determination of thallium in complex matrices the procedure for elimination of interferences from foreign ions exploiting anion exchange resin was proposed. The procedure proposed was validated by analysis of rain water certified reference material. 相似文献
90.
A novel procedure for the extraction of soluble, sparingly soluble and insoluble Cr(VI) from solid samples was presented. EDTA was added to an ammonia buffer commonly used only for the extraction of soluble and sparingly soluble Cr(VI). In the course of extraction in an ultrasonic bath cations which form insoluble chromates are complexed with EDTA while Cr(VI) is transferred to the solution. A concentration of EDTA equal to 0.01 mol L−1 was chosen. The presence of EDTA in the extraction solution enables not only dissolution of insoluble Cr(VI) but also, as reported previously in literature, minimises oxidation of Cr(III) to Cr(VI). The extraction procedure was optimised and applied to Cr(VI) determination in the paint chips real sample. The results obtained were compared with the results obtained using two other extraction procedures. The results show that the novel extraction procedure can be used for the extraction of soluble, sparingly soluble and insoluble Cr(VI) from real solid samples. 相似文献