Brown T L, Rice J A
Department of Chemistry and Biochemistry, South Dakota State University, Brookings 57007-0896.
Anal Chem. 2000 Jan 15;72(2):384-90. doi: 10.1021/ac9902087.
Fulvic acid (FA) is a heterogeneous mixture of organic macromolecules found in the waters, soils, and sediments of the earth's surface. The ability of electrospray ionization (ESI) to effectively transfer large ions from the solution phase to the gas phase and the coupling of ESI to the high-mass-resolution capabilities of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provide a potential method for the mass spectrometric analysis of FA. Positive- and negative-ion ESI FT-ICR MS analyses of four reference International Humic Substances Society FAs were performed. The spray solution composition was found to have a dramatic effect on the ion distributions, with high-mass aggregates (m/z approximately 2000-4000) being formed in less polar spray solutions. Positive-ion spectra for each FA obtained under optimum conditions resulted in number-average molecular weights ranging from 1700 to 1900. The mass spectra were extremely complex, with ion distributions on the order of m/z approximately 500-3000. The presence of more than one ion at each nominal mass was routinely observed. Negative-ion ESI analysis of the FA samples resulted in the observation of multiply charged ions whose distributions could be affected by the acidification of the spray solution. Solution parameters which have been reported to affect molecular weight distributions of FA such as pH, ionic strength, and concentration of multivalent cations were found to have little or no effect on the observed m/z distributions.
富里酸（FA）是一种存在于地球表面水体、土壤和沉积物中的有机大分子的非均相混合物。电喷雾电离（ESI）能够有效地将大离子从溶液相转移到气相，并且ESI与傅里叶变换离子回旋共振质谱（FT-ICR MS）的高质量分辨率能力相结合，为富里酸的质谱分析提供了一种潜在的方法。对国际腐殖质协会的四种参考富里酸进行了正离子和负离子ESI FT-ICR MS分析。发现喷雾溶液组成对离子分布有显著影响，在极性较小的喷雾溶液中会形成高质量聚集体（m/z约为2000 - 4000）。在最佳条件下获得的每种富里酸的正离子谱，其数均分子量范围为1700至1900。质谱极其复杂，离子分布在m/z约为500 - 3000的量级。通常在每个标称质量处观察到不止一个离子。对富里酸样品的负离子ESI分析导致观察到多电荷离子，其分布可能受喷雾溶液酸化的影响。据报道会影响富里酸分子量分布的溶液参数，如pH值、离子强度和多价阳离子浓度，对观察到的m/z分布几乎没有影响或没有影响。
