3D-fluorescence spectroscopic analysis of HPLC fractionated estuarine fulvic and humic acids

Abstract

Seis amostras de ácidos fúlvicos (AF) e húmicos (AH) estuarinos foram fracionadas por meio de cromatografia líquida de alta performance em fase reversa, num gradiente de polaridade água → acetonitrila, com detecção por fluorescência. Diferenças entre os cromatogramas mostraram que os AH contêm mais componentes hidrofóbicos que os AF. Os espectros de fluorescência tridimensional das frações foram bastante similares entre si e também ao da amostra original, indicando que, apesar das polaridades distintas, a complexidade e as principais características do material original se mantêm. Um mesmo grupo de fluoróforos parece ser responsável pelas características de fluorescência, dos dois tipos de substâncias húmicas. Um deslocamento batocrômico dos espectros de emissão das soluções originais, com relação àqueles das frações, foi atribuído a uma maior proximidade destes fluoróforos, possivelmente devido à formação de agregados. Em geral, os resultados confirmam o conceito de que as "macromoléculas" húmicas consistem de associações de estruturas menores com características químicas semelhantes.Six estuarine fulvic (FA) and humic acids (HA) were fractionated with reversed-phase high performance liquid chromatography in a water/acetonitrile gradient, with fluorescence detection. Differences between FA and HA chromatograms pointed to a higher incidence of hydrophobic components in the latter. Excitation-emission matrix fluorescence diagrams of most fractions were similar to those of the bulk samples indicating that, in spite of their distinct polarities, the complexity and main spectral characteristics of the materials persisted. A primary group of fluorophores, which are present in most of the fractions, seems to be at the origin of the fluorescence properties of both kinds of HS. A bathochromic shift of the bulk solutions spectra in relation to the fraction emissions was attributed to a greater proximity of these fluorophores, possibly due to the formation of aggregates. Generally, the results reinforced concepts that humic macromolecules consist of assemblages of structurally similar building blocks. Keywords: RP-HPLC, fulvic acids, humic acids, EEM fluorescence IntroductionHumic substances (HS) are complex macromolecular products resulting from the chemical and biological degradation of plant and animal residues. They are widely distributed in soils, natural waters, and sediments, and represent a significant proportion of the organic carbon in the global carbon cycle.1-4 According to current estimates, HS constitute the major fraction of soil organic matter (up to 80%) and the largest fraction of natural organic matter (NOM) in aquatic systems (up to 60% of dissolved organic carbon). 5,6These organic materials can have a substantial impact on a variety of biogeochemical processes, for example, immobilizing anthropogenic organic chemicals and heavy metals. 7-11The elucidation of the HS molecular sizes, shapes, weights and structural arrangements is essential for an [15][16][17][18][19] In general, UV absorbance, and/or ...

Humic substances and aggregate stability in rhizospheric and non-rhizospheric soil

“…By applying the high-performance liquid chromatography (HPLC) method, one can divide the molecules of HAs into fractions that are hydrophobic and hydrophilic in nature (Woelki et al 1997;Preuße et al 2000;Sierra et al 2006;Dębska et al 2010Dębska et al , 2012). An additional aspect of the study of HAs is the determination of the value of absorbance at 465 nm (A 465 ) and 665 nm (A 665 ) and the absorbance ratio A 4/6 (Jing-an et al 2007; Kalembasa and Becher 2009;KondratowiczMaciejewska et al 2011) which can be used to estimate the maturity of the HAs (Polak et al 2011) and as an indicator of the degree of organic matter humification.…”

Potentiometric acidity determination in humic substances influenced by different analytical procedures

“…Modeling such interactions requires, among other parameters, accurate determination of acid-base properties (concentrations and equilibrium constants). [1][2][3][4][5][6][7][8][9] A major fraction of dissolved OM in natural ecosystems is in fact formed by humic substances (HS), which are characterized by the presence of several functional groups with labile protons such as carboxylic acids, phenols and amines. These moieties are able to bind protons and metal cations that not only affect the geochemistry of natural systems, but also regulate the buffer capacity of waters, soils and sediments, and metal speciation and transport.…”

“…[1][2][3][4][5] The assessment of concentrations and equilibrium constants of carboxylic and phenolic groups is, therefore, a key step in the characterization of acidity, ion exchange capacity, and charge development properties of HS systems. 3,[6][7][8][9] Within this context, two main approaches have been employed in the determination of acid contents of fulvic acid (FA) and humic acid (HA) systems: indirect and direct titrations. In the first case, the analyses consist in the titration of filtered reaction mixtures to a fixed pH end-point after a 24 h equilibrium time with either barium hydroxide or calcium acetate, and have the advantage of simplicity.…”

Estudo da matéria orgânica e composição elementar de solos arenosos de regiões próximas a São Gabriel da Cachoeira no Amazonas

“…Usualmente os espectros bidimensionais de fluorescência podem ser adquiridos de três modos: emissão, excitação e varredura sincronizada (Senesi, 1992 (McKnight et al, 2001;Tanoue, 2001;Chen et al, 2002Chen et al, , 2003, identificando as fontes de MON, monitorando as contaminações nas águas naturais e, em estudos de fracionamento de SH só apareceram recentemente na literatura (Sierra, 2006;Liu et al, 2009). …”