No presente trabalho foram extraídas substâncias húmicas aquáticas através do uso da resina adsorvente XAD 8, e a fração ácida separada por acidificação. Depois da purificação com resina Hyphan e diálise, os ácidos húmicos aquáticos foram caracterizados por espectroscopia no infravermelho com transformada de Fourier e análise elementar. A influência das concentrações dos ácidos húmicos e eletrólitos, pH e tempo de complexação ácido húmico-metal sobre a conformação estrutural foi investigada através de estudos de espectroscopia UVVis, empregando a equação sugerida por Doty e Steiner. Os resultados indicam que a macromolécula flexível do ácido húmico assume uma forma condensada em valores de pH ácidos e alcalinos. Outros fatores favorecendo formas condensadas são tempos de complexação mais longos, e altas concentrações de ácidos húmicos e eletrólitos. Assim, considerando a forte influência dos parâmetros investigados na conformação estrutural da macromolécula húmica, podemos concluir que estudos usando espectroscopia UV/Vis para determinar a concentração, aromaticidade e grau de humificação dos ácidos húmicos aquáticos, requerem condições rigorosamente controladas para garantir uma correta interpretação dos resultados analíticos.In the present work, aquatic humic substances (HS) were extracted by use of adsorbent XAD 8 and the acid humic fraction (AH) was separated throught acidification. After being purified by Hyphan resin and dialyze, the aquatic AH was characterized using Fourier-transform infrared spectroscopy and elemental analysis. The influence of the aquatic HA and electrolyte concentrations, pH and aquatic AH-metal complexation time on the conformation was investigated using UV/Vis spectroscopic studies, employing the equation suggested by Doty and Steiner. The results indicated that the acid humic flexible macromolecule assumes a condensed form at acid and alkaline pH. Other factors favoring condensed conformations are longer metal complexation time ("ageing") and higher aquatic AH and electrolyte concentrations. Thus considering the strong influence of the investigated parameters in the structural conformation of the humic macromolecule, we conclude that studies using UV/Vis spectroscopy to estimate the concentration, aromaticity, humification degree of the aquatic AH and so on, require rigorous control over the experimental conditions employed to provide a correct interpretation of the analytical results.
As substâncias húmicas aquáticas investigadas foram convencionalmente extraídas de amostra de água coletada no Rio Negro -AM, Brasil utilizando-se resina XAD 8. Investigações usando ressonância nuclear magnética de próton e carbono treze indicaram a presença de alta aromaticidade com pouca substituição, pequena quantidade carbono carboxílico e razão 1:1 de grupos alifáticos / aromáticos. A razão das absorbâncias E350/E450, na região do ultravioleta e do visível, sugere a presença de estruturas alifáticas em proporções relativamente grandes. A distribuição do peso molecular das substâncias húmicas aquáticas foi caracterizada utilizando-se um sistema de ultra filtração de 5 estágios. O fracionamento indicou que metais traço, originalmente complexados com as substâncias húmicas, apresentam diferentes distribuições.The aquatic humic substances investigated in this study were conventionally isolated from Rio Negro waters -Amazonas State/Brazil by means of the collector XAD 8. Molecular spectroscopy investigations of these humic substances using 1 H-NMR and 13 C-NMR indicated the presence of high aromaticity with few substituents, small amounts of carboxylic carbon, and an aliphatic/aromatic ratio of 1:1. The relatively high UV-VIS absorbance E350/E450 ratio suggested the presence of relatively large proportions of aliphatic structures. Moreover, using a five-stage tangential-flow ultrafiltration (UF) device, the molecular-size distribution of the isolated humic substances was characterized. The fractionation patterns showed that metal traces remaining in humic substances after their XAD 8 isolation have different size distributions. For instance, Mn, Cu, Cd and Ni quantified by ICP-AES were preferably found in the high molecular-weight fractions (10-100 kDa).
Recebido em 13/5/10; aceito em 12/1/11; publicado na web em 29/3/11In this study Ucides cordatus crab shells were utilized as Fe (II) sorbent as material of low cost and simple preparation. Values of pH of standard solution, biosorbent mass, particles size, contact time (t c ) and initial concentration of the standard solution were optimized. The best conditions were pH = 2.00, t c = 840 min and M c = 0.25 g. The kinetic pseudo first-order model displayed the best description of the adsorption process and the equilibrium study showed that the Langmuir model better describes the adsorption of the Fe (II). There is great affinity between the Fe (II) and the biosorbent.
Abstract. Enzyme-Linked Immunosorbent Assay (ELISA) has been evaluated by analyzing rich-humic water samples from tropical r ivers. The samples were spiked with atrazine at ppb level. Different pHs (4 to 9) and humic concentrations (2.5 to 40 mg L -1 ) were investigated. The assay performance showed a strong dependence on the pH values and amount of humic matter at low atrazine concentration. F rom all the conditions studied the low pH (pH 4) and high humic substances concentrations (40 mg L to humic acid solution. This effect is specially noted for the humic acid fractions, since fulvic acid fractions showed no significant change on the immunoassay results. Additionally, it has been demonstrated that at basic pH the matrix effect produced by the natural Brazilian water sample containing humic substances even at 40 mg L -1 disappears. Therefore, the ELISA method used to determine atrazine, can be employed to determine this pesticide in water samples containing humic substances without prior preparation.
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