38 research outputs found

    Purification, Recovery, and Laser-Driven Fluorination of Silicon from Dissolved and Particulate Silica for the Measurement of Natural Stable Isotope Abundances

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    International audienceA procedure for the purification, recovery, and determination of isotopic abundances of silicon from biogenic and lithogenic particulate matter and dissolved silicic acid is reported. Purification involves the reaction of acid molybdate with dissolved silicon in natural waters or that produced by the dissolution of particulate silica by hydrofluoric acid. The resulting silicomolybdic acid is then quantitatively precipitated by reaction with triethylamine hydrochloride. The silicon is recovered as silicon dioxide through stepwise combustion of the dried precipitate. Fluorination of the product for isotopic analysis is accomplished by laser heating under pure fluorine generated by the decomposition of a fluorine-based salt. The resulting silicon tetrafluoride is separated from hydrogen fluoride and other fluorination byproducts cryogenically using a variable-temperature cold trap. Yields for silicon recovery are 99.9% for precipitation and greater than 95% for the purification /fluorination procedure. Reproducibility of the isotopic composition for pure quartz granules processed through the procedure is +_0.1‰ for d30Si

    A first look at the distribution of the stable isotopes of silicon in natural waters

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    International audienceThe first data on the distribution of the stable isotopes of silicon in marine and freshwater systems are reported. Both marine and riverine d30Si are more positive than d30Si of igneous rocks, suggesting isotopic fractionation during weathering and clay formation and/or biomineralization. The d30Si value for dissolved silicic acid from several ocean basins is 11.1 6 0.3‰ (n 5 69). More positive values are found in surface waters, due to discrimination against 30Si during biogenic opal formation by diatoms. The deep Pacific Ocean is depleted in 30Si relative to the deep Atlantic by roughly 0.4‰. d30Si of riverine dissolved silicon averages 10.8 6 0.3 (n 5 8). The biologic fractionation of silicon isotopes coupled with effects associated with thermohaline circulation appears to play a significant role in controlling the distribution of silicon isotopes in the sea. The average d30Si value of inputs of silicon to the ocean most likely falls between 10.3 and 10.9‰, and that of the outputs falls between 10.9 to 11.9‰, probably in the neighborhood of 11.0‰

    Fractionation of silicon isotopes by marine diatoms during biogenic silica formation

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    International audienceThe fractionation of silicon isotopes by three species of marine diatoms, Skeletonema costatum, Thalassiosira weissflogii, and Thalassiosira sp., grown in batch culture, is reported. Fractionation was observed for all species. The d30Si value of the diatom silica and that of the initial silicic acid in the culture medium were used to compute a fractionation factor (a). The values of a for the three species were nearly identical, averaging 0.9989 _+ 0.0004 (s.d., n = 13), which corresponds to the production of diatom silica with a d30Si value that is 1.1%o more negative than that of the dissolved silicon utilized for growth. The fractionation factor did not vary with temperature and the consequent change in growth rate (ANOVA, p = 0.61; tested at 12 °C, 15 °C, and 22°C with Thalassiosira sp.). The observation of fractionation of silicon isotopes by diatoms is an essential step in establishing d30Si variations in biogenic silica as a potential oceanographic tracer

    Rastreabilidade da farinha de carne e ossos bovinos em ovos de poedeiras comerciais pela tĂ©cnica dos isĂłtopos estĂĄveis do carbono e nitrogĂȘnio Traceability of bovine meat and bones meal in eggs of commercial laying hens through carbon and nitrogen stable isotopes technique

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    Objetivou-se com este estudo rastrear a inclusĂŁo de farinha de carne e ossos bovinos em dietas para poedeiras comerciais, por meio da anĂĄlise dos ovos e de suas fraçÔes (gema e albĂșmen), pela tĂ©cnica dos isĂłtopos estĂĄveis do carbono e nitrogĂȘnio e avaliar o Ă­ndice analĂ­tico mĂ­nimo detectĂĄvel. Foram utilizadas 240 galinhas poedeiras da linhagem Shaver White de 73 semanas de idade, distribuĂ­das em delineamento inteiramente casualizado, com cinco tratamentos e seis repetiçÔes. Foram avaliados cinco nĂ­veis de inclusĂŁo (0; 1,5; 3,0; 4,5 e 6,0%) de farinha de carne e ossos bovinos em uma dieta Ă  base de milho e farelo de soja. No 35Âș dia, foram tomados aleatoriamente 24 ovos por tratamento: 12 serviram para amostragem de gema e albĂșmen e os outros 12 para amostragem do ovo (gema + albĂșmen). Os resultados isotĂłpicos foram submetidos Ă  anĂĄlise multivariada de variĂąncia e, a partir das matrizes de erro, com 95% de confiança, foram determinadas elipses para identificar as diferenças entre os resultados obtidos com o fornecimento das dietas experimentais e a dieta controle, sem farinha de carne e ossos bovinos. No ovo e na gema, a partir do par isotĂłpico da dieta com 3,0% de farinha de carne e ossos, houve diferenciação do par do tratamento controle, enquanto, no albĂșmen, a diferenciação ocorreu a partir do nĂ­vel de 1,5% de farinha de carne e ossos bovinos na dieta. Pela tĂ©cnica dos isĂłtopos estĂĄveis, Ă© possĂ­vel rastrear o uso de farinha de carne e ossos bovinos na alimentação de poedeiras; no albĂșmen, o nĂ­vel mĂ­nimo de inclusĂŁo detectĂĄvel Ă© de 1,5% e, no ovo e na gema, 3,0%.<br>The objective of this study was to trace the inclusion of bovine meat and bones meal in diets of laying hens analyzing eggs and theirs fractions (yolk and albumen), by carbon and nitrogen stable isotopes, as well as to evaluate the detectable analytical minimal index. Two hundred and forty (240) Shaver White laying hens aging 73 weeks were distributed in a completely randomized design, with five treatments and six replicates. Five increasing levels (0; 1.5; 3.0; 4.5 and 6.0%) of bovine meat and bones meal in a diet based on corn and soybean meal were evaluated. On the 35th day, 24 eggs per treatment were randomly collected, twelve for yolk and albumen sampling and another twelve for egg (yolk + albumen) sampling. The isotopic results were analyzed in a multivariate analysis of variance. Through an error matrix (95% confidence) the ellipses were determined to identify the differences between results obtained with supply of experimental diets and control diet, without 3% bovine meat and bones meal. In egg and yolk, from the isotopes pair of the diet with 3% bovine meat and bones meal, there was differentiation in the pair of the control treatment, whereas in the albumen it was possible to detect the 1.5 bovine meat and bones meal. The stable isotopes technique is able to trace the use of bovine meat and bones meal in laying hens feed; the minimal traceable level of inclusion is 1.5% in the albumen and 3.0% in the egg and yolk
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