Application of the Three-dimensional Excitation-emission Matrix Fluorescence Spectroscopy in the Analysis of Soil Dissolved Organic Matter Components
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摘要: 土壤溶解性有机质是具有较高化学和微生物活性的土壤有机质组分,其周转在维持土壤肥力和调节生态系统碳循环中发挥着核心作用,正确解析可溶性有机质的化学组分对深刻理解其生态环境效应具有重要意义。 论文旨在概述常见的土壤可溶性有机质组分分析方法,简要比较了常见的可溶性有机质化学组分分析技术,包括紫外-可见吸收光谱法、傅里叶红外光谱法、核磁共振法、傅里叶回旋共振质谱法和三维荧光光谱法的基本原理及技术优缺点,并着重对三维荧光光谱法在土壤可溶性有机质组分解析应用过程中的重要影响因素、常用荧光指标和数据处理方法进行了综述。三维荧光光谱法具有操作简便、仪器可及性高、成本低、通量高等特点,通过荧光指数、腐殖化指数及生物源指数等表征指标追溯土壤可溶性有机质的来源,结合平行因子分析法解析可溶性有机质化学组分及其对土地利用方式、耕种制度、全球变化因子的响应。但是,三维荧光光谱法也存在易受环境影响、解谱困难等局限性。未来研究亟需定量分析环境因素对可溶性有机质荧光特性的影响,并加强与其它分析技术和方法的联用,有助于更准确和全面地解析可溶性有机质,继而深入理解其生态环境效应。Abstract: Dissolved organic matter (DOM) is a labile and reactive fraction of soil organic matter. The molecular characterization of DOM is helpful to clarify its ecological and environmental effects, especially its pivotal role in soil fertility and carbon cycling in the context of global environmental change. This paper aims to summarize the common analytical methods of DOM, the basic principles and applications of Ultraviolet-Visible Spectroscopy, Fourier Transform Infrared Spectroscopy, Nuclear Magnetic Resonance Spectroscopy, Fourier Transform Ion Cyclotron Resonance Mass Spectrometry and Three-dimensional Excitation-Emission Matrix Fluorescence Spectroscopy (3D-EEM). The important influencing factors, common fluorescence indices and data processing methods of Three-dimensional Excitation-Emission Matrix Fluorescence Spectroscopy in the application of soil DOM component analysis were emphatically reviewed. Among these techniques, 3D-EEM has the merits of easy operation, simple configuration, high throughput as well as low cost and has been widely applied for the source identification by fluorescence index, humification index and biological source index. Moreover, the chemical components of DOM and their responses to land use patterns, farming systems and global change factors can be analyzed by parallel factor analysis. However, the 3D-EEM also has the limitations of being susceptible to environmental impact and difficulty in spectrum analysis. Future research needs to quantitatively analyze the influence of environmental factors on the fluorescence characteristics of DOM, to strengthen the combination with other analytical techniques and methods of more accurately and comprehensively determining the DOM components, and further to understand its ecological and environmental effects.
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Key words:
- Dissolved organic matter /
- Component analysis /
- 3D-EEM
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表 1 DOM组分分析常用方法对比
Table 1. Comparison of various instruments for analysis of DOM composition
分析方法
Method of analysis应用原理
Application principle特点
Characteristics局限
Limitation紫外-可见吸收光谱(UV-Vis) 样品经紫外/可见光照射时,某些官能团中的价电子从低能级跃迁到高能级的过程中会吸收特定波长的光,从而形成光谱图 较早用于表征DOM光谱特征的方法之一,仪器普及率高、操作简便、分析快捷[23-24] 可直接获得的信息有限,多用紫外特征参数(如SUVA值、S值等)表征DOM芳香性、疏水性、腐殖化程度、分子量大小等信息[25],表征参数的适用范围和适用性有待深入探讨 傅里叶红外光谱(FTIR) 基于物质分子化学键对红外光的选择性吸收,当红外辐射到被测样品时,一部分红外辐射会被官能团的特定共价键吸收,另一部分则直接穿透捕获到光谱 重复性好、信噪比好、分辨率高、杂散光影响小、光通量大[26-28] 通常需要把样品干燥并碾磨成固体粉末后测定,以避免水对红外光谱的吸收干扰测定[29];需对测定数据进行求导或去卷积处理从而解析光谱[30] 核磁共振(NMR) 基于原子核的自旋运动,13C、1H等自旋量子数I(表示不同原子核的自旋运动情况)不为零的原子核在外界磁场会发生进动[31-33],在此过程中吸收与原子核进动频率相同的射频辐射发生塞曼分裂(原子的光谱线在外磁场中所出现的分裂),随后从自旋能级跃迁到塞曼能级,从而产生相应的核磁共振信号[31-32] 对样品无损耗、非侵入,可用于液态和固态样品的测定 仪器成本和维护费用较高,测定时需注意:利用1H-NMR测定样品所用的溶剂不可含H,以免干扰;样品检测前或需进行适当的提取分离等预处理手段[33] 傅里叶变换离子回旋共振质谱(FT-ICR MS) 基于离子在均匀磁场中的回旋运动,当对离子施加与其回旋频率相同的射频时,离子受激发运动至半径较大的回旋轨道上,从而产生电流信号。采用的射频范围覆盖了样品测定的质量范围时,所有离子同时受到激发,检测得到的信号经傅里叶变换即可转换为质谱图 [34-35] 具有超高的质量分辨率和精确度;无需将离子分离,在同一时间内可以同时检测不同离子的质荷比及相对丰度[36] 难以反映化合物的结构信息,无法区分同分异构体;仪器购置、运行及维护成本较高[37-38] 三维荧光光谱法(3D-EEM) 分子吸收能量(电能、热能、化学能、光能等)后由基态跃迁至激发态,在由不稳定激发态衰变回基态过程中产生荧光 灵敏度高、无需化学试剂、样品需求量少且对样品无破坏[21-22,39] 解谱及分析方法有待改进,DOM的表征参数范围有待统一 -
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