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1.
Several extraction procedures are described allowing arsenic speciation in sediments. The extraction of organometallic compounds
such as dimethylarsinic acid or monomethylarsonic acid is quite simple since these compounds are stable in the different extraction
media (HCl/ HNO3, H3PO4, ammonium oxalate) and are easily released independent of the extraction mode (magnetic stirring or microwave solubilization).
Extraction yields are higher than 96% for these two arsenic forms. An HCl/HNO3 microwave solubilization procedure allows the quantitative solubilization of mineral arsenic, but the differentiation between
the two oxidation states is not possible owing to the oxidation of As(III) to As(V). Extractions with orthophosphoric acid
or ammonium oxalate allow the solubilization of mineral arsenic with extraction yields ranging from 90 to 95% and the differentiation
between As(III) and As(V). Nevertheless, the amount of As(III) is underestimated owing to its partial oxidation. The usefulness
and advantages of microwave solubilization compared with conventional extraction procedures are discussed.
Received: 17 May 1996 / Revised: 19 September 1996 / Accepted: 25 September 1996 相似文献
2.
—The results of two studies are reported. In the first study, the carotenoid pigments, β-carotene. canthaxanthin and phytoene were administered to mice after one UV-B-induced skin tumor had developed, to see if carotenoid administration would delay the development of subsequent tumors. Canthaxanthin significantly delayed the development of subsequent tumors. In the second study, the same pigments were administered starting 10 weeks before, and for 24 weeks after, exposure to a large single fluence (8 × 104 J/m2 ) of UV-B radiation, to determine the effect of the pigments on tumor development. Phytoene significantly prevented the development of tumors to this fluence of radiation. 相似文献
3.
Micheline Grignon-Dubois Jacques Dunogues Raymond Calas 《Journal of organometallic chemistry》1979,181(2):285-291
Studies of the electrophilic substitution on two 1-sila-3-cyclopentenes and their cyclopropane homologues revealed the important role of silicon and provided a new route to alkenylfluorosilanes and novel β,γ or especially γ,δ-unsaturated silylated ketones. 相似文献
4.
Abstract— Phytoene, the colorless triene precursor of β-carotene (17 mg/g body weight) or a placebo was given to guinea pigs by daily intraperitoneal injection for 14 days, after which the animals were exposed to radiation (> 280 nm). It was found that the animals receiving phytoene developed significantly less erythema to the radiation than did the animals receiving placebo. 相似文献
5.
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7.
Norbert De Kimpe Roland Verhé Laurent De Buyck Niceas Schamp Micheline Charpentier-Morize 《Tetrahedron letters》1982,23(28):2853-2856
α-Chloroaldimines are arylated at the α-position under Friedel-Crafts conditions via intermediacy of α-imidoylcarbenium ions. 相似文献
8.
The stoichiometric lanthanum disulfide LaS2 presents a reversible phase transition at about 750°C. The α low-temperature form is monoclinic with the LaSe2 type. All the crystals are twinned with the same twin law (100). The cell parameters are a = 8.18, b = 8.13, c = 4.03Å, γ = 90°, space group . The β high-temperature form has the orthorhombic structure previously described with the parameters a = 8.13, b = 16.34, c = 4.14 Å; space group Pnma. The two structures are compared. 相似文献
9.
Lévêque JM Desset S Suptil J Fachinger C Draye M Bonrath W Cravotto G 《Ultrasonics sonochemistry》2006,13(2):189-193
The replacement of common organic solvents by room-temperature ionic liquids (RTILs) is a topical subject in both academia and industry. In the last decades, the number of applications for RTILs has followed an exponential curve and spilled over the boundaries of chemistry. Still, one of the main drawbacks of these compounds is their difficult access. The present ultrasound-assisted method affords a general and easy access to a large variety of room-temperature ionic liquids. 相似文献
10.