Radiochemical Approach for Studying Properties of Humic Substances (original) (raw)
Related papers
A new technique for tritium labeling of humic substances
Radiochimica Acta, 2010
Humic substances (HS) of different origins have been labeled with tritium by the thermal activation method. Specific radioactivity of labeled HS ( 3 H-HS) was sufficiently high and varied from 0.05 to 0.6 TBq/g. Parent HS and 3 H-HS were analyzed by size exclusion chromatography with radioactivity and UV detection. The results allowed concluding that (1) neither partial decomposition nor polymerization of HS occurred during labeling and (2) tritium labeled molecules have a regular distribution among HS fractions of different molecular weights. The performed correlation analysis revealed that there was no significant relationship between HS properties and specific radioactivity of the obtained 3 H-HS. Thus universality of the developed technique for radioactive labeling of HS with tritium could be demonstrated.
Radioisotopes and Analytical Chemistry
World Journal of Nuclear Science and Technology, 2013
When Periodic Chart of elements is consulted to find natural radioisotopes, one firstly finds tritium, followed by 10 Be, 14 C, 50 V and many others. Before Bi, 12 cosmogenic radioisotopes are listed. They are those continuously produced by nuclear reactions among light elements present in earthly atmosphere and radiations coming from the outside space. Eighteen additional primordial radioisotopes are listed. They were created at the same time that the non-radioactive isotopes composing the 92 natural elements in the periodic table. From Bi on, every isotope is radioactive, up to U. Then follow the artificial elements produced by laboratory nuclear reactions from Np to element with atomic number 118. In this way, from 118 known elements, 64 are radioactive, which amount 55% of all those units forming the chemical compounds. Therefore, the complete understanding of radioactivity should be a suitable tool to advance our knowledge of Universe, and consequent applications to get better living conditions. So, this paper deals with radioisotopes as suitable instruments for chemical analysis.
Journal of Nuclear Medicine, 1983
International Atomic Energy Agency, 825 pp. $104.00 This book contains the proceedings of the International Sym posiumon Radioimmunoassay and Related Procedures in Medi cine held by the IAEA in Vienna from June 21-25, 1982. Included are the texts of 76 presentations (nine of which are reviewpapers, 23 of which are posters)togetherwith editedsummariesof the
Changes of AhR-mediated activity of humic substances after irradiation
Environment International, 2007
Humic substances (HS) and natural organic matter (NOM) are natural organic compounds ubiquitous in the environment. However, some studies indicate that both HS and NOM can act as xenobiotics, e.g. induce hormone-like effects in fish, amphibians and invertebrates. Molecules of these substances contain a number of aromatic rings and conjugated double bondsthe so called chromophores. Irradiation of dissolved HS and NOM can lead to a series of photochemical reactions which can act on these substances itself, or on other substances present in aquatic environment along with HS and NOM such as e.g. xenobiotics. In our previous study, we have found significant interactions of five humic acids (HA) with cytosolic aryl hydrocarbon receptor (AhR) in an in vitro bioassay based on H4IIE-luc cells. In the present study, we have studied the changes in AhR-mediated activities both of HS and NOM after irradiation that simulated natural solar light. Nine different HS and two NOM samples were irradiated in Pyrex tubes with a medium-pressure mercury lamp for a duration of 0 to 52 h (which corresponds to 0-52 d natural solar radiation). Original concentrations of the samples were 50 mg L − 1 , and the greatest concentration of HS and NOM photoproducts subsequently tested in the bioassay was 17 mg L − 1 , which is an environmentally relevant concentration. After irradiation the absorbances of all the samples were less than the original materials. The AhR-mediated activity of the HA-Fluka and HA Sodium Salt were partially decreased by irradiation. The activities of other HS and NOM, that were either AhR-active or-inactive were not changed by irradiation. The results of the study demonstrate that AhR-mediated activities of two active HA is caused by both photo-stable and photo-labile AhR activators, while the other three active HA contain only photo-stable AhR activators. Potential mechanisms of the observed irradiation-induced changes in AhR-mediated activities are discussed.
Radioactive labelling and characterisation of humic materials
Environment International, 1994
Humic acids can radiolabelled either by chemical techniques, either with iodine or with carbon-14. This paper discusses the advantages and disadvantages of the different labelling techniques for chemical radiolabelling of humic materials as well as the optimum conditions for the labelling. Various techniques have been applied in order to characterize the labelled material to elucidate possible changes of the inherent characteristics of the humic acids introduced during the labelling process. These techniques comprise ultrafiltration, e.g. size fractionation, metal complexing ability, UV absorbance and fluorescence, and DEAE cellulose abstraction. It has been demonstrated that with respect to these features, the radiolabelling techniques do not alter the humic acid molecules.
Aspects of protonation and deprotonation of humic scid durface on molecular conformation
Journal of the Brazilian Chemical Society, 2011
As densidades superficiais de carga de ácidos húmicos foram determinadas por titulação potenciométrica e condutimétrica simultâneas. Também foi observada a influência do pH na conformação molecular através de espectroscopia de UV-Vis e microscopia eletrônica de varredura (MEV). A densidade de carga superficial para todas as amostras de ácido húmico é aproximadamente zero na faixa de pH 3,5-6,0. A influência do pH na condensação molecular foi observada pela determinação do índice b na equação de Doty e Steiner. Os altos valores de b foram obtidos na região ácida, indicando uma conformação condensada, devido à fraca interação atrativa. Além disso, na região alcalina, a densidade de carga na superfície da molécula é mais negativa, o que favorece o aumento da repulsão e dispersão das partículas, levando à formação de estruturas micelares como consequência da característica anfifílica dos ácidos húmicos. The surface charge densities for humic acids (HAs) were determined by simultaneous potentiometric and conductimetric titrations. It was also observed the pH influence on molecular conformation by UV-Vis spectroscopy measurements and scanning electron microscopy (SEM) images. The surface charge densities are approximately zero at the pH range 3.5 to 6.0 for all samples. The pH influence on molecular condensation level was observed by the determination of the b index from Doty and Steiner equation. High values of b were obtained at acid region indicating a condensed conformation due to weak attractive interactions whereas around the neutral region the repulsive intramolecular forces take place leading to an extended conformation of humic molecules. Moreover, at very alkaline region, the charge density on molecule surface is more negative, increasing repulsion and dispersion of the particles and also takes place formation of micelle-like structure because of the amphyphylic feature of HA samples.
1970
X 'pathfinders' for uranium. This also applied to other trace elements involved in the metabolism of the plant. Uranium is not only radioactive, but poisonous as well, and its toxic effects on metabolism are usually more significant than the radiation it produces. How can a plant survive the absorption of such an element? Research was obviously needed here. Such avenues of basic research were considered essential to a continuing expansion of knowledge concerning the factors that enable plants to be used in biogeochemical prospecting. The aims of the thesis were thus specifically: (i) To develop a routine, but sensitive assay for uranium. on the basis 10 4. Dissolution of plant ash and soils Plant ash was dissolved in 3 M nitric acid, as it has been shown by Geiger (1 959) that this treatment solubilises almost all uranium. Soils, however, required digestion with ten times their weight of 1:1 hydrochloric-hydrofluoric acid mixture. The mixture was evaporated to dryness in 15ml polypropylene beakers partially immersed in a water bath, and redissolved in 15ml of 3 M nitric acid. The suitability of the method was checked by analysis in triplicate of CAAS syenite (Webber, 1965) for which uranium values of 2,890 ppm were obtained (recommended range 2, 230-3, 000 ppm). It was concluded that this method of dissolution was adequate.