Maastricht MultiModal Molecular Imaging (M4I) institute, Division of Imaging Mass Spectrometry, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands.
Shell Global Solutions International B.V., Grasweg 31, 1031 HW Amsterdam, The Netherlands.
J Am Soc Mass Spectrom. 2020 Nov 4;31(11):2356-2361. doi: 10.1021/jasms.0c00290. Epub 2020 Oct 9.
Time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging provides molecular speciation at the micrometer scale, while the penetration depth of the primary ion beam is limited to the top-layers of a sample. These combined properties make TOF-SIMS potentially an ideal technique to study oil-gas interfaces. TOF-SIMS spectra of three crude oils were evaluated, and only low-mass fragment ions could be assigned to molecular structures unambiguously. Films of crude oils were incubated under air, oil vapor, or water vapor for various times. TOF-SIMS images of a polar crude oil revealed feeble structures of ∼10 μm large round patches that grew to ∼30 μm large crystals when incubated under air and oil vapor, respectively. Principal component analysis of the images showed that the continuous phase had typical aromatic signatures, while the patches and crystals had alkane-like characteristics. No features showed up when the oil film was incubated under water vapor, which indicated that saturated water vapor prevented the accumulation of nonpolar alkane-like compounds at the oil-gas interface. These examples showed that crude oils do not behave as dead fluids but that their constituents accumulate at the oil-gas interfaces in a dynamic way.
飞行时间二次离子质谱（TOF-SIMS）成像可在微米尺度上提供分子形态，而初级离子束的穿透深度仅限于样品的顶层。这些综合特性使 TOF-SIMS 成为研究油气界面的理想技术。评估了三种原油的 TOF-SIMS 光谱，只有低质量碎片离子可以明确分配给分子结构。将原油薄膜在空气、油蒸气或水蒸气中孵育不同时间。在空气和油蒸气中分别孵育时，极性原油的 TOF-SIMS 图像显示出微弱的约 10 μm 大的圆形斑块结构，这些斑块分别生长至约 30 μm 大的晶体。对图像进行主成分分析表明，连续相具有典型的芳香特征，而斑块和晶体则具有烷烃特征。当油膜在水蒸气中孵育时，没有出现特征，这表明饱和水蒸气阻止了非极性烷烃类化合物在油气界面处的积累。这些例子表明，原油并非死水，而是其成分以动态方式在油气界面处积累。
