Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, USA.
Anal Chem. 2013 Jun 18;85(12):6100-6. doi: 10.1021/ac400976z. Epub 2013 May 30.
Soil organic matter (SOM) is important because its decay drives life processes in the biosphere. Analysis of organic compounds in geological systems is difficult because of their intimate association with mineral surfaces. To date there is no procedure capable of quantitatively separating organic from mineral phases without creating artifacts or mass loss. Therefore, analytical techniques that can (a) generate information about both organic and mineral phases simultaneously and (b) allow the examination of predetermined high-interest regions of the sample as opposed to conventional bulk analytical techniques are valuable. Laser desorption synchrotron postionization (synchrotron-LDPI) mass spectrometry is introduced as a novel analytical tool to characterize the molecular properties of organic compounds in mineral-organic samples from terrestrial systems, and it is demonstrated that, when combined with secondary ion mass spectrometry (SIMS), it can provide complementary information on mineral composition. Mass spectrometry along a decomposition gradient in density fractions verifies the consistency of our results with bulk analytical techniques. We further demonstrate that, by changing laser and photoionization energies, variations in molecular stability of organic compounds associated with mineral surfaces can be determined. The combination of synchrotron-LDPI and SIMS shows that the energetic conditions involved in desorption and ionization of organic matter may be a greater determinant of mass spectral signatures than the inherent molecular structure of the organic compounds investigated. The latter has implications for molecular models of natural organic matter that are based on mass spectrometric information.
土壤有机质（SOM）很重要，因为它的分解驱动着生物圈中的生命过程。由于其与矿物表面的密切关系，分析地质系统中的有机化合物是困难的。迄今为止，还没有一种能够在不产生人为产物或质量损失的情况下定量分离有机相与矿物相的方法。因此，能够（a）同时生成有关有机相和矿物相的信息，以及（b）允许检查样品中预定的高兴趣区域的分析技术，而不是传统的批量分析技术，是有价值的。激光解吸同步辐射后电离（同步辐射-LDPI）质谱被引入作为一种新的分析工具，用于表征来自陆地系统的矿物-有机样品中有机化合物的分子特性，并且证明，当与二次离子质谱（SIMS）结合使用时，它可以提供关于矿物成分的互补信息。沿密度分数的分解梯度进行质谱分析验证了我们的结果与批量分析技术的一致性。我们进一步证明，通过改变激光和光离化能量，可以确定与矿物表面相关的有机化合物的分子稳定性的变化。同步辐射-LDPI 和 SIMS 的组合表明，有机质解吸和离化所涉及的能量条件可能比所研究的有机化合物的固有分子结构更能决定质谱特征。后者对基于质谱信息的天然有机质分子模型具有影响。
