电喷雾质谱和钌离子催化氧化法研究腐殖酸分子结构特征
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摘要
腐殖酸是自然环境中广泛存在的一类天然有机大分子物质,对环境中的碳循
环,有机、无机化合物在自然界的分布、迁移、转化和归宿,以及土壤中的矿物
组成和土壤肥力有非常重要的影响。腐殖酸的这些行为都与其结构有密切关系,
因此对腐殖酸的分子结构特征的研究有非常重要的意义。
本文采用电喷雾质谱(ESI-MS)技术,对水溶态Pahokee泥炭腐殖酸的结
构特征进行了研究,突破了以往固态腐殖酸样品的限制。利用钌离子催化氧化法
(RICO)对两个泥炭腐殖酸(PILAI和PHAII)、两个土壤腐殖酸(SHAI和SIIAII)
和一个商业腐殖酸(AHA)中以C-C_(arom)键结合的烷基侧链以及它们的芳香核的
缩合程度进行了表征。
ESI-MS质谱图中,离子峰连续分布,m/z值主要集中在低于1500的范围内,
在质谱图低质荷比端形成相差2个amu的奇数系列峰,可能为复杂分子峰【M-1】
的系列中性丢失的结果;在m/z约250,350,500和700处有类似“波”的离子
峰分布,可能暗示不同来源的木质素单体形成的二聚体、三聚体、四聚体结构等。
根据木质素类17种模型化合物的电喷雾二级质谱碎片机理的详细研究,推断出
了腐殖酸m/z200以内离子峰的结构。m/z70-110为Pahokee泥炭腐殖酸的“核结
构”,m/z110-200主要为三种木质素来源的单体结构及其衍生物,总体上可看出
Pahokee泥炭腐殖酸的母源为裸子植物和被子植物。
RICO产物中,直链一元脂肪酸是降解产物中最丰富的一类, 除商业腐殖酸
以C_(28)酸丰度最高外,其它四种腐殖酸的C_(16)酸丰度非常高,都具有明显的偶奇
优势。一元脂肪酸的碳数范围为C_7C_(34),则与芳核相连的烷基侧链的长度为
C_6-C_(33)。PHAI、SHAI和SHAII样品的一元脂肪酸具有双峰型的分布特征。样品
AHA主要为长链的一元脂肪酸(>C_(20))。除PHAI外,其它的腐殖酸未检测到二
元脂肪酸。其中C_(14)-C_(18)脂肪酸中,可能会含有少量游离态脂肪酸,但主要还是
以结合态为主。腐殖酸RICO产物中还检测到藿烷酸甲酯化合物,分布范围为
C_(28)-C_(31)(C_(29)缺失)。藿烷酸甲酯化合物都只有一个R构型,即生物构型,暗示
腐殖酸具有极低的成熟度。共检测出13种芳羧酸产物,1-6个羧基,腐殖酸的苯
Humic acids are a group of natural organic macromolecules and ubiquitous in the environment. They play an important role in global carbon cycle, affect the distribution, fate, transport, and bioavailability of organic and inorganic pollutants. In addition, they are involved in the mineral composition of soil and the improvements of the soil fertility. All these behaviors are related to their structural composition. Therefore, it has a great significance to characterize the molecular structures of humic acids.The structural characterizations of aqueous humic acid from Pahokee peat was conducted by Electrospray Ionization Mass Spectrometry (ESI-MS). This method avoided the limitation of other analytical methods for solid samples. The verification of side alkyl substitutes bonding to aromatic rings (Calkyl-Carom) in five humic acids, which are two peat humic acids (PHAI and PHAII), two soil humic acids (SHAI and SHAII) and a commercial humic acid (AHA) were characterized using Ruthenium Ion Catalyzed Oxidation (RICO) method. The aromatic structures of humic acids were also discussed in this study.The ion peaks distributed continuously with the mass charge ratios, with most ion fragments below m/z 1500. The two atomic mass unit difference of the odd ion peaks in the low mass charge ratios resulted from neutral mass lose of complex molecular. The strength of ion peaks was characterized by "wave pattern" maxima at
m/z 250, 350, 500 and 700, representing that the dimeric, trimeric and tetrameric structures of lignin degraded products. Based on ESI-MS/MS mechanism of 17 model compounds of lignin monomers, the structures of ion fragments between m/z 70 and 200 was deduced. M/z 70-110 were the "core structure" of Pahokee humic acid, while m/z 110-200 were mainly the monomer of p-hydroxy phenols, vanillyl phenols, syringyl phenols and their derivations. So, the parent source were gymnosperm and angiosperm.n-Alkanoic acids were the major components in the RICO products of humic acids, with obviously odd/even predominance. The highest abundances of four natural humic acids were the n-C16 acid, whereas n-C26 acid for commercial sample AHA. Carbon numbers of monocarboxylic acids range from C7 to C34, consequently the carbon numbers of side alkyl chain bonding to aromatic rings were C6 to C33. The distributions of n-alkanoic acid for PHAI, SHAI, and SHAII were characterized by bimodal peak, whereas AHA was characterized by unimodal distribution with long chain alkanoic acids (>C20). Alkyl-a, ω-dicarboxylic acids were only detected in sample PHAI. Most of n-alkanoic acids ranging from C14 to C18 were bonding to aromatic rings (Calkyl-Carom) as side alkyl substitutes, whereas few of them are occurred as free fatty acid. Hopane acid methyl esters were firstly founded in humic acids, which ranged from C28 to C31 with exception for C29. Hopane acid methyl esters had only R configuration, i.e., organism configuration, suggesting that the maturity of humic acids was low. Thirteen kinds of aromatic carboxylic acids (1-6 carboxyl groups) were also detected in these humic acids. Aromatic tetracarboxylic acid and pentacarboxylic acid were relatively high in four of five humic acids, showing that more polycyclic aromatic hydrocarbons such as anthracene, phenanthrene, triphenylene existed. Relatively high contents of aromatic hexacarboxylic acid implied that more complex PAH such as triphenylene, dibenxopyrene, coronene and perylene existed in humic acids.
环,有机、无机化合物在自然界的分布、迁移、转化和归宿,以及土壤中的矿物
组成和土壤肥力有非常重要的影响。腐殖酸的这些行为都与其结构有密切关系,
因此对腐殖酸的分子结构特征的研究有非常重要的意义。
本文采用电喷雾质谱(ESI-MS)技术,对水溶态Pahokee泥炭腐殖酸的结
构特征进行了研究,突破了以往固态腐殖酸样品的限制。利用钌离子催化氧化法
(RICO)对两个泥炭腐殖酸(PILAI和PHAII)、两个土壤腐殖酸(SHAI和SIIAII)
和一个商业腐殖酸(AHA)中以C-C_(arom)键结合的烷基侧链以及它们的芳香核的
缩合程度进行了表征。
ESI-MS质谱图中,离子峰连续分布,m/z值主要集中在低于1500的范围内,
在质谱图低质荷比端形成相差2个amu的奇数系列峰,可能为复杂分子峰【M-1】
的系列中性丢失的结果;在m/z约250,350,500和700处有类似“波”的离子
峰分布,可能暗示不同来源的木质素单体形成的二聚体、三聚体、四聚体结构等。
根据木质素类17种模型化合物的电喷雾二级质谱碎片机理的详细研究,推断出
了腐殖酸m/z200以内离子峰的结构。m/z70-110为Pahokee泥炭腐殖酸的“核结
构”,m/z110-200主要为三种木质素来源的单体结构及其衍生物,总体上可看出
Pahokee泥炭腐殖酸的母源为裸子植物和被子植物。
RICO产物中,直链一元脂肪酸是降解产物中最丰富的一类, 除商业腐殖酸
以C_(28)酸丰度最高外,其它四种腐殖酸的C_(16)酸丰度非常高,都具有明显的偶奇
优势。一元脂肪酸的碳数范围为C_7C_(34),则与芳核相连的烷基侧链的长度为
C_6-C_(33)。PHAI、SHAI和SHAII样品的一元脂肪酸具有双峰型的分布特征。样品
AHA主要为长链的一元脂肪酸(>C_(20))。除PHAI外,其它的腐殖酸未检测到二
元脂肪酸。其中C_(14)-C_(18)脂肪酸中,可能会含有少量游离态脂肪酸,但主要还是
以结合态为主。腐殖酸RICO产物中还检测到藿烷酸甲酯化合物,分布范围为
C_(28)-C_(31)(C_(29)缺失)。藿烷酸甲酯化合物都只有一个R构型,即生物构型,暗示
腐殖酸具有极低的成熟度。共检测出13种芳羧酸产物,1-6个羧基,腐殖酸的苯
Humic acids are a group of natural organic macromolecules and ubiquitous in the environment. They play an important role in global carbon cycle, affect the distribution, fate, transport, and bioavailability of organic and inorganic pollutants. In addition, they are involved in the mineral composition of soil and the improvements of the soil fertility. All these behaviors are related to their structural composition. Therefore, it has a great significance to characterize the molecular structures of humic acids.The structural characterizations of aqueous humic acid from Pahokee peat was conducted by Electrospray Ionization Mass Spectrometry (ESI-MS). This method avoided the limitation of other analytical methods for solid samples. The verification of side alkyl substitutes bonding to aromatic rings (Calkyl-Carom) in five humic acids, which are two peat humic acids (PHAI and PHAII), two soil humic acids (SHAI and SHAII) and a commercial humic acid (AHA) were characterized using Ruthenium Ion Catalyzed Oxidation (RICO) method. The aromatic structures of humic acids were also discussed in this study.The ion peaks distributed continuously with the mass charge ratios, with most ion fragments below m/z 1500. The two atomic mass unit difference of the odd ion peaks in the low mass charge ratios resulted from neutral mass lose of complex molecular. The strength of ion peaks was characterized by "wave pattern" maxima at
m/z 250, 350, 500 and 700, representing that the dimeric, trimeric and tetrameric structures of lignin degraded products. Based on ESI-MS/MS mechanism of 17 model compounds of lignin monomers, the structures of ion fragments between m/z 70 and 200 was deduced. M/z 70-110 were the "core structure" of Pahokee humic acid, while m/z 110-200 were mainly the monomer of p-hydroxy phenols, vanillyl phenols, syringyl phenols and their derivations. So, the parent source were gymnosperm and angiosperm.n-Alkanoic acids were the major components in the RICO products of humic acids, with obviously odd/even predominance. The highest abundances of four natural humic acids were the n-C16 acid, whereas n-C26 acid for commercial sample AHA. Carbon numbers of monocarboxylic acids range from C7 to C34, consequently the carbon numbers of side alkyl chain bonding to aromatic rings were C6 to C33. The distributions of n-alkanoic acid for PHAI, SHAI, and SHAII were characterized by bimodal peak, whereas AHA was characterized by unimodal distribution with long chain alkanoic acids (>C20). Alkyl-a, ω-dicarboxylic acids were only detected in sample PHAI. Most of n-alkanoic acids ranging from C14 to C18 were bonding to aromatic rings (Calkyl-Carom) as side alkyl substitutes, whereas few of them are occurred as free fatty acid. Hopane acid methyl esters were firstly founded in humic acids, which ranged from C28 to C31 with exception for C29. Hopane acid methyl esters had only R configuration, i.e., organism configuration, suggesting that the maturity of humic acids was low. Thirteen kinds of aromatic carboxylic acids (1-6 carboxyl groups) were also detected in these humic acids. Aromatic tetracarboxylic acid and pentacarboxylic acid were relatively high in four of five humic acids, showing that more polycyclic aromatic hydrocarbons such as anthracene, phenanthrene, triphenylene existed. Relatively high contents of aromatic hexacarboxylic acid implied that more complex PAH such as triphenylene, dibenxopyrene, coronene and perylene existed in humic acids.
引文
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