The characteristics of subfractions of soil fulvic acid (FA3, FA5, FA7, FA9, and FA13) using stepwise elution from XAD-8 resin with pyrophosphate buffers were investigated by differential absorption spectroscopy (DAS) and differential fluorescence spectroscopy (DFS) combined with mathematical deconvolution and spectral indices. The log-transformed absorbance spectra (LTAS) exhibited three regions for both acidic-buffer-eluted subfractions (AESF) and neutral-buffer-eluted subfraction (NESF) and four regions for basic-buffer-eluted subfractions (BESF) according to the differences in spectral slopes. The DAS spectra of FA subfractions were closely fitted with seven Gaussian bands with maxima location at 199.66, 216.18 ± 1.50, 246.20 ± 3.85, 285.22 ± 7.26, 345.64 ± 5.30, 389.27, and 307.37 nm, respectively (R2 > 0.993). The content of salicylic-like and carboxyl groups in FA subfractions decreased, while the phenolic chromophore increased with elution sequence. From the 11 spectral indices, AESF had greater molecular weight, condensation, polymerization, hydroxyl radical production, humification degree, and terrigenous contribution, as well as contained more conjugated aromatic structures and less N-containing groups than NESF and BESF. The humification degree and humic characters of FA subfractions were closely associated to the aromaticity, molecular condensation, and DOM-metal-bound functional groups. The proper separation of FA into subfractions is beneficial for reducing its complexity and heterogeneity, which helps us to further explore its chemical properties and interactions with various contaminants in soil environments. Graphical abstract.

中文翻译：

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利用差分光谱结合高斯反卷积和光谱指数研究富里酸的洗脱特性。

通过差示吸收光谱法（DAS）和差示荧光光谱法（DFS）结合数学方法，研究了使用焦磷酸缓冲液从XAD-8树脂中逐步洗脱得到的土壤黄腐酸（FA3，FA5，FA7，FA9和FA13）的亚组分的特征。去卷积和频谱指数。对数转换后的吸收光谱（LTAS）分别显示了酸性缓冲液洗脱亚级分（AESF）和中性缓冲液洗脱亚级分（NESF）的三个区域和碱性缓冲液洗脱亚级分（BESF）的四个区域在频谱斜率上。FA亚组分的DAS光谱与七个高斯谱带紧密拟合，最大带分别位于199.66、216.18±1.50、246.20±3.85、285.22±7.26、345.64±5.30、389.27和307.37 nm（R2> 0.993）。FA洗脱液中水杨酸样和羧基的含量随洗脱顺序的增加而降低，而酚类发色团的含量随洗脱顺序的增加而增加。从11个光谱指数来看，与NESF和BESF相比，AESF具有更大的分子量，缩合度，聚合度，羟基自由基产生，腐殖度和陆源性贡献，并且包含更多的共轭芳族结构和更少的含N基团。FA组分的腐殖化程度和腐殖质特性与芳香性，分子缩合和DOM-金属结合的官能团密切相关。正确地将FA分离为亚组分有利于降低其复杂性和异质性，这有助于我们进一步探索其化学性质以及与土壤环境中各种污染物的相互作用。图形概要。