Department of Chemistry, Higher Polytechnic School, University of Burgos, Av. Cantabria s/n, 09006 Burgos, Spain.
Department of Chemistry & Biology, Faculty of Mathematics and Natural Science, University of Wuppertal, Germany.
Sci Total Environ. 2014 Apr 1;476-477:718-30. doi: 10.1016/j.scitotenv.2013.11.150. Epub 2013 Dec 21.
The main objective of this work (Part I) is to conduct a comprehensive structural characterization of humic substances, using all the current fluorescence techniques: emission scan fluorescence (ESF), synchronous fluorescence spectroscopy (SFS), total luminescence spectroscopy (TLS or EEM) through the use of both 2-D contour maps and 3-D plots, fluorescence index and the λ0.5 parameter. Four humic substances were studied in this work: three of them were provided by the International Humic Substances Society (Suwannee River Fulvic Acid Standard, Suwannee River Humic Acid Standard and Nordic Reservoir Fulvic Acid Reference) and the other one was a commercial humic acid widely used as a surrogate for aquatic humic substances in various studies (Aldrich Humic Acid: ALHA). The EEM spectra for the three natural aquatic substances were quite similar, showing two main peaks of maximum fluorescence intensity: one located in the ultraviolet region and centered at around Ex/Em values of 230/437 nm (peak A) and another one in the visible region, centered at around 335/460 nm (peak C); however, the EEM spectrum of ALHA is completely different to those of natural aquatic humic substances, presenting four poorly resolved main peaks with a high degree of spectral overlap, located at 260/462, 300/479, 365/483 and 450/524 nm. The synchronous spectra at Δλ=18 and 44 nm (especially at Δλ=18 nm) allowed the identification of a protein-like peak at λsyn around 290 nm, which was not detected in the EEM spectra; as it happened with EEM spectra, the synchronous spectra of ALHA are quite different from those of the aquatic humic substances, presenting a higher number of bands that suggest greater structural complexity and a higher degree of polydispersity. Good correlations were achieved between (13)C NMR aromaticity and both fluorescence index and λ0.5 parameter. The different spectra presented by ALHA compared to those shown by the natural aquatic humic substances for all the fluorescence techniques studied suggest an important structural difference between them, which cast doubt on the use of commercial humic acids as surrogates for natural humic substances.
本工作（第一部分）的主要目标是使用所有当前的荧光技术对腐殖质进行全面的结构表征：发射扫描荧光（ESF）、同步荧光光谱法（SFS）、全荧光光谱法（TLS 或 EEM），同时使用二维等高线图和三维图、荧光指数和 λ0.5 参数。本工作研究了四种腐殖质：其中三种由国际腐殖质协会提供（苏万尼河富里酸标准、苏万尼河腐殖酸标准和北欧水库富里酸参考物质），另一种是商业腐殖酸，广泛用作各种研究中水生腐殖质的替代物（Aldrich 腐殖酸：ALHA）。三种天然水生生物质的 EEM 光谱非常相似，显示出两个最大荧光强度的主峰：一个位于紫外区，中心在 Ex/Em 值约为 230/437nm（峰 A），另一个位于可见区，中心在约 335/460nm（峰 C）；然而，ALHA 的 EEM 光谱与天然水生生物质的光谱完全不同，呈现出四个分辨率较低的主峰，具有高度的光谱重叠，位于 260/462、300/479、365/483 和 450/524nm。Δλ=18 和 44nm 的同步光谱（特别是在 Δλ=18nm 时）允许在 λsyn 约 290nm 处识别出类蛋白峰，该峰在 EEM 光谱中未检测到；与 EEM 光谱一样，ALHA 的同步光谱与水生生物质的光谱有很大的不同，呈现出更多的带，表明结构更复杂，多分散性更高。（13）C NMR 芳香度与荧光指数和 λ0.5 参数之间实现了良好的相关性。与所有研究的荧光技术相比，ALHA 呈现的不同光谱与天然水生生物质呈现的光谱表明它们之间存在重要的结构差异，这使人对将商业腐殖酸用作天然腐殖质的替代品产生了怀疑。
