Department of Chemistry & Biochemistry, Florida International University, 3000 NE 151 Street, Biscayne Bay Campus, North Miami, Florida 33181, USA.
Department of Chemistry & Biochemistry, Florida International University, 3000 NE 151 Street, Biscayne Bay Campus, North Miami, Florida 33181, USA; Southeast Environmental Research Center (SERC), Florida International University, 3000 NE 151 Street, Biscayne Bay Campus, North Miami, Florida 33181, USA.
Sci Total Environ. 2016 Oct 15;568:1018-1025. doi: 10.1016/j.scitotenv.2016.06.044. Epub 2016 Jun 28.
Understanding the composition of crude oil and its changes with weathering is essential when assessing its provenience, fate, and toxicity. High-resolution mass spectrometry (HRMS) has provided the opportunity to address the complexity of crude oil by assigning molecular formulae, and sorting compounds into "classes" based on heteroatom content. However, factors such as suppression effects and discrimination towards certain components severely limit a truly comprehensive mass spectrometric characterization, and, despite the availability of increasingly better mass spectrometers, a complete characterization of oil still represents a major challenge. In order to fully comprehend the significance of class abundances, as well as the nature and identity of compounds detected, a good understanding of the ionization efficiency of the various compound classes is indispensable. The current study, therefore, analyzed model compounds typically found in crude oils by high-resolution mass spectrometry with atmospheric pressure photoionization (APPI), atmospheric pressure chemical ionization (APCI), and electrospray ionization (ESI), in order to provide a better understanding of benefits and drawbacks of each source. The findings indicate that, overall, APPI provides the best results, being able to ionize the broadest range of compounds, providing the best results with respect to ionization efficiencies, and exhibiting the least suppression effects. However, just like in the other two sources, in APPI several factors have shown to affect the ionization efficiency of petroleum model compounds. The main such factor is the presence or absence of functional groups that can be easily protonated/deprotonated, in addition to other factors such as size, methylation level, presence of heteroatoms, and ring structure. Overall, this study evidences the intrinsic limitations and benefits of each of the three sources, and should provide the fundamental knowledge required to expand the power of crude oil analysis by high-resolution mass spectrometry.
了解原油的组成及其风化过程中的变化，对于评估其来源、归宿和毒性至关重要。高分辨率质谱（HRMS）提供了一种机会，可以通过分配分子公式，根据杂原子含量将化合物分类为“类”，从而解决原油的复杂性问题。然而，抑制效应和对某些成分的歧视等因素严重限制了真正全面的质谱特征描述，而且，尽管有越来越先进的质谱仪可供使用，对油的全面特征描述仍然是一个主要挑战。为了充分理解类丰度的意义，以及检测到的化合物的性质和身份，必须很好地了解各种化合物类别的电离效率。因此，本研究通过大气压光致电离（APPI）、大气压化学电离（APCI）和电喷雾电离（ESI）对原油中典型的模型化合物进行了高分辨率质谱分析，以便更好地了解每种源的优缺点。研究结果表明，总体而言，APPI 提供了最佳结果，能够电离最广泛的化合物范围，在电离效率方面提供了最佳结果，并表现出最小的抑制效应。然而，与其他两种源一样，APPI 有几个因素已被证明会影响石油模型化合物的电离效率。主要因素是存在或不存在可以容易质子化/去质子化的官能团，此外还有其他因素，如大小、甲基化水平、杂原子存在和环结构。总的来说，本研究证明了这三种源的内在局限性和优势，应该为通过高分辨率质谱扩展原油分析能力提供所需的基本知识。
