Tracking Neutral Nitrogen Compounds in Subfractions of Crude Oil Obtained by Liquid Chromatography Separation Using Negative-Ion Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass
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- 作者：Yahe Zhang ; Chunming Xu ; Quan Shi ; Suoqi Zhao ; Keng H. Chung ; Dujie Hou
- 刊名：Energy & Fuels
- 出版年：2010
- 出版时间：December 16, 2010
- 年：2010
- 卷：24
- 期：12
- 页码：6321-6326
- 全文大小：838K
- 年卷期：v.24,no.12(December 16, 2010)
- ISSN：1520-5029
文摘
Neutral nitrogen compounds have been used as molecular markers for tracking secondary oil migration in geochemistry. However, the distribution of neutral nitrogen compounds in the separation process is not well-characterized because the conventional analytical technique, such as gas chromatography−mass spectrometry (GC−MS), is non-selective for neutral nitrogen and not capable of detecting non-volatile high-molecular-weight compounds. In this paper, a crude oil was subjected to the traditional two-step open-column liquid chromatography (LC) technique to prepare subfractions, which were characterized for their molecular composition of neutral nitrogen compounds by negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The results showed that the two-step LC technique produced a low yield of carbazole in the neutral nitrogen fraction. The neutral nitrogen fraction was enriched with low-molecular-weight neutral nitrogen compounds. Most N1 class species with relatively low double-bond equivalent (DBE) values and high carbon numbers were eluted into the aromatic fraction, and a portion of neutral nitrogen compounds was eluted into the amino fraction, which was not expected. Because the neutral nitrogen compounds detected by GC−MS analysis only account for a fraction of total neutral nitrogen compounds, caution should be exercised in interpreting the analytical data obtained from the two-step LC technique. The analytical bias of the separation technique could lead to erroneous geochemical interpretations when a low yield of carbazole in the neutral nitrogen fraction was derived. Negative-ion ESI FT-ICR MS was an effective tool to monitor and evaluate the separation technique for neutral nitrogen compounds in crude oil.