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 Spectrometry

Abstract

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 N 1 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.

Insight into the structural features of Zhaotong lignite using multiple techniques

“…In all the N 1 O x class species, pyrroles are the typical nitrogen compounds that can be efficiently ionized via deprotonation in negative-ion mode, which was confirmed by many ESI FT-ICR MS studies [38,39]. Only 4 types (DBE = 6, 7, 9, and 10) of NNCs were detected in N 1 class, in which species with DBE = 6 and 9 should be ascribed to indoles and carbazoles, respectively.…”

Characterization of Extracts from Geting Bituminous Coal

“…These results may suggest that most aromatic ring-containing species in Geting bituminous coal are macromolecular species. A more obvious difference is present in the absorbances around 1040, 910, 540, and 470 per centimeter, which are caused by the presence of mineral matter (Zhang et al 2010;Zhang et al 2011). Figure 6 shows that the organic species significantly decreased with increased extraction times.…”

Introduction to Oil Chemistry and Properties Related to Oil Spills

“…The branching potential for alkanes increases as the size of the alkane increases. Table 4 shows the typical alkanes contained in crude oils and some fuels (Wang et al 1993(Wang et al : 2003CRC 2016CRC -2017Yalkowsky et al 2010;Mackay et al 1992;Verchueren 2001;Faksness et al 2010;Wang and Brown 2008). Some properties and content of n-alkanes in some crude oils are also shown in this table.…”