Fluorescence et propriétés photochimiques des matières organiques naturelles (original) (raw)
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Re sume ÐLes eaux de¯euve, fractionne es par ultra®ltration tangentielle se quentielle (UFTS), sont ana-lyse es par des matrices d'excitation et d'e mission de¯uorescence (MEEF). Les substances humiques uorescentes provenant des eaux du bassin amazonien, sont caracte rise es par les longueurs d'onde d'excitation et d'e mission des intensite s de¯uorescence maximum sur des diagrammes 3D (l ex /l em ) et du rapport des intensite s de¯uorescence (r a,c =I a /I c ) de deux¯uorophores (type humique A et C) dans les eaux naturelles. Les re sultats obtenus montrent que: (i) des espeÁ ces¯uorescentes provenant d'eaux riches en mate riel humique (eaux noires) sont pre fe rentiellement retenues par le seuil de coupure de 5 kDa (type humique C). Ces compose s de type C ont une masse mole culaire plus e leve e que les com-pose s¯uorescents de type humique A. (ii) Les re actions de complexation avec les ions cuivriques (Cu 2+ ) se parent les compose s humiques de type C en deux cate gories: l'une ne variant pas, l'autre e largissant le domaine des longueurs d'onde d'excitation ecaces de 20 nm. La photolyse produit des eets similaires sur les compose s humiques de type C. A partir des donne es spectroscopiques et des masses mole culaires, une tentative d'identi®cation est propose e pour les¯uorophores A (l 260 /l 445 ) et C (l 350 / l 445 ). Les compose s de type A et C manifestent des caracte ristiques qui les rapprochent respectivement des acides fulviques et des acides humiques. # AbstractÐNatural organic matter is an important pool that is not yet totally described. Two types of compounds are found: some chemically well characterised molecules (biopolymers) and uncharacterised humic substances (geopolymers). The spectroscopic properties of this pool of organic matter have recently been advanced by the excitation emission¯uorescence matrix (EEFM) Characterization of marine and terrestrial DOM in seawater using excitation-emission matrix spectroscopy. Marine Chemistry 51, 325±346.]. Three types of¯uorophores are described by their excitation/emission wavelength at maximum intensity (l ex /l em ) max : the tyrosin and tryptophan like structures, not examined here, and the humic like¯uorescent structures of type A (l 260 /l 445 ) and type C (l 330 /l 445 ). The EEFM applied to sequential tangential ultra®ltered (UFTS) amazonian fresh waters give spectroscopic information on the¯uorescent properties of particulate (>0.22 mm), colloidal and dissolved (<5 kDa) organic matter. Chromophores A and C are present in all sized fraction samples. Their (l ex /l em ) max are in the same domains as those of terrestrial humic substances [Seritti, A., Morelli, E., Nannicini, L. and Del Vecchio, R. (1994) Production of hydrophobic¯uorescent organic matter by marine diation Pheodactylum tricornutum. Chemosphere 28(1), 117±129; Coble, G. P. (1996) Characterization of marine and terrestrial DOM in seawater using excitation-emission matrix spectroscopy. Marine Chemistry 51, 325±346.]. Dierentiation of the type A and type C peaks in 3D diagrams are based on their (l ex /l em ) max position and the I a /I c ratio. Dierences are observed between humic material extracted by hydrophobic resins or concentrated sample from tangential sequential ultra®ltration (UFTS). Spectroscopic properties of the humic material are not modi®ed by the ultra®ltration process. A particular attention is given on the dierentiation between black water (Rio Negro River) and white water (Rio SolimoÄ es and Rio Madeira River). Black waters are generally known as humic rich and low mineral content waters. EEFM analysis on these two types of water lead to the following conclusions: (i) the humic like¯uorescent compounds of type C are preferentially retained by membranes with 5 kDa cut o. These compounds have the larger molecular weight. (ii) In the presence of copper cation, the type C compounds are divided in two groups according to their (l ex /l em ) max : the ®rst one is invariant, the other one expands (20 nm) its ecient excitation wavelength domain. (iii) Photochemical reactions induced by UV irradiation also lead to a 20 nm expansion of the ecient excitation wavelength domain. From these spectroscopic and molecular weight complementary data, it is proposed that A type¯uorophores are close to fulvic acids while C¯uorophores seems to be more related to humic acid. #
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