Natural Organic Matter and the Event Horizon of Mass Spectrometry
Natural Organic Matter and the Event Horizon of Mass Spectrometry
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DOI：
10.1021/ac800464g
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发表时间：
2008-12-01
影响因子：
7.4
通讯作者：
Perdue, E. M.
中科院分区：
文献类型：
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作者：
Hertkorn, N.;Frommberger, M.;Perdue, E. M.
土壤、沉积物、沃茨和海洋沃茨中含有天然有机物（NOM），这是一种极其复杂的有机化合物混合物，它们共同表现出几乎连续的性质（尺寸-反应性连续体）。NOM主要由碳、氢和氧组成，杂原子如氮、硫和磷的贡献较小。Suwannee River富里酸（SuwFA）是NOM的一部分，其相对缺乏杂原子。超高分辨率傅里叶变换离子回旋（FTICR）质谱的SuwFA揭示了几千个分子式，反过来对应于几十万个不同的化学环境的碳，即使没有会计的异构体。相邻的C，H，O-分子之间的标称质量的集群和集群内的质量差Am是负相关的分子相异性：任何减少的Am强加一个不断增长的强制性差异的分子组成。预期可能的生化前体分子的分子式明显不存在于这些光谱中，这表明SuwFA是成岩反应的产物，该反应改变了生物质的主要成分，超出了识别点。SuwFA的复杂程度可以通过与化学复杂性的理论极限进行比较而变得清晰，因为化学结合的基本原理限制和量化。理论上的C，H，O-组成空间是指完全由碳、氢和氧组成的分子结构的整个非常广阔的空间的异构体过滤补充。SuwFA中的分子式占据了理论C，H，O-组成空间的相当大的比例。在相当大的质量和H/C和O/C元素比范围内，通过SuwFA分子实现理论上可行的C，H，O-组成空间的100%覆盖。使用六种不同的电离模式（APCI，APPI和ESI的正和负模式）观察到的SuwFA分子式之间的实质性差异（和互补性）意味着相当大的电离过程的选择性，并表明所观察到的质谱表示简化的投影更复杂的混合物。
Soils, sediments, freshwaters, and marine waters contain natural organic matter (NOM), an exceedingly complex mixture of organic compounds that collectively exhibit a nearly continuous range of properties (size-reactivity continuum). NOM is composed mainly of carbon, hydrogen, and oxygen, with minor contributions from heteroatoms such as nitrogen, sulfur, and phosphorus. Suwannee River fulvic acid (SuwFA) is a fraction of NOM that is relatively depleted in heteroatoms. Ultrahigh resolution Fourier transform ion cyclotron (FTICR) mass spectra of SuwFA reveal several thousand molecular formulas, corresponding in turn to several hundred thousand distinct chemical environments of carbon even without accountancy of isomers. The mass difference Am among adjoining C,H,O-molecules between and within clusters of nominal mass is inversely related to molecular dissimilarity: any decrease of Am imposes an ever growing mandatory difference in molecular composition. Molecular formulas that are expected for likely biochemical precursor molecules are notably absent from these spectra, indicating that SuwFA is the product of diagenetic reactions that have altered the major components of biomass beyond the point of recognition. The degree of complexity of SuwFA can be brought into sharp focus through comparison with the theoretical limits of chemical complexity, as constrained and quantized by the fundamentals of chemical binding. The theoretical C,H,O-compositional space denotes the isomer-filtered complement of the entire, very vast space of molecular structures composed solely of carbon, hydrogen, and oxygen. The molecular formulas within SuwFA occupy a sizable proportion of the theoretical C,H,O-compositional space. A 100 percent coverage of the theoretically feasible C,H,O-compositional space by SuwFA molecules is attained throughout a sizable range of mass and H/C and O/C elemental ratios. The substantial differences between (and complementarity of) the SuwFA molecular formulas that are observed using six different modes of ionization (APCI, APPI, and ESI in positive and negative modus) imply considerable selectivity of the ionization process and suggest that the observed mass spectra represent simplified projections of still more complex mixtures.