Stenson Alexandra C, Landing William M, Marshall Alan G, Cooper William T
Department of Chemistry and Biochemistry, Florida State University, Tallahassee 32306, USA.
Anal Chem. 2002 Sep 1;74(17):4397-409. doi: 10.1021/ac020019f.
Electrospray ionization (ESI) was combined with ultra-high-resolution Fourier transform-ion cyclotron resonance mass spectrometry (FTICR MS) to characterize complex humic and fulvic acid mixtures. Lower than expected molecular weight distributions previously observed for humics when analyzed by ESI-MS have fueled speculation about a bias in favor of low molecular weight. Multiply charged ions, ionization suppression, and sample fragmentation have all been suggested as sources of this low molecular weight bias. In this work, resolution of the individual components of humic mixtures within a 1 mass-to-charge unit window was accomplished by FTICR MS at 9.4 T. At mass resolving powers between 60,000 (high mass) and 120,000 (low mass), it was possible to determine that virtually all ions present in spectra of Suwannee River fulvic and humic acid are singly charged, thus eliminating inadequate accounting for multiply charged ions as a primary source of any low molecular weight bias. The high-resolution mass spectra also revealed the presence of molecular families containing ions that differ from each other in degree of saturation, functional group substitution (primarily CH vs N and CH4 vs O), and number of CH2 groups. Ionization suppression and ion fragmentation were addressed for humic and fulvic acid mixtures and well-characterized poly(ethylene glycol) (PEG) mixtures with average molecular weights of 8000 and 10,000. Although these high molecular weight PEG mixtures fragment extensively under traditional positive-ion mode ESI conditions, similar fragmentation could not be confirmed for humic and fulvic acid mixtures.
电喷雾电离（ESI）与超高分辨率傅里叶变换离子回旋共振质谱（FTICR MS）相结合，用于表征复杂的腐殖酸和富里酸混合物。以前通过ESI-MS分析腐殖质时观察到的分子量分布低于预期，这引发了关于偏向低分子量的猜测。多电荷离子、电离抑制和样品碎片化都被认为是这种低分子量偏差的来源。在这项工作中，通过9.4 T的FTICR MS在1个质荷比单位窗口内实现了腐殖质混合物中各个组分的分离。在60,000（高质量）至120,000（低质量）的质量分辨率下，可以确定苏万尼河富里酸和腐殖酸光谱中几乎所有存在的离子都是单电荷的，从而消除了将多电荷离子的计算不足作为任何低分子量偏差的主要来源。高分辨率质谱还揭示了存在分子家族，这些分子家族中的离子在饱和度、官能团取代（主要是CH与N以及CH4与O）和CH2基团数量上彼此不同。针对腐殖酸和富里酸混合物以及平均分子量为8000和10,000的特征明确的聚乙二醇（PEG）混合物，研究了电离抑制和离子碎片化问题。尽管这些高分子量PEG混合物在传统正离子模式ESI条件下会大量碎片化，但腐殖酸和富里酸混合物并未出现类似的碎片化现象。
