Extended characterization of petroleum aromatics using off-line LC-GC-MS

Crude oil remains a grand challenge for analytical chemists. With the advent of multi-dimensional chromatography and high-resolution mass spectrometry, an impressive number of compounds have been identified. However, the large diversity in structure and abundance makes it difficult to obtain full compound coverage in a single analysis. Sample preparation methods such as solid-phase extraction and SARA-type analysis reduces this complexity. However, the molecular diversity within each fraction is still highly complex. Thus, in the routine analysis, only a small part of the chemical space is typically characterized. Obtaining a more detailed composition of crude oil is important for production, processing and environmental aspects. We have developed a high-resolution fractionation method for isolation and preconcentration of trace aromatics, including oxygenated and nitrogen-containing species. By the isolation of the more abundant aromatics, i.e. monoaromatics and naphthalenes, trace species can be enriched for analysis. This enables the identification of features not detectable by routine methods. We demonstrate the applicability by fractionation and subsequent GC-MS analysis of 14 crude oils sourced from the North Sea. The number of tentatively identified compounds increased by approximately 60 to 150% compared to solid-phase extraction and GC×GC-MS. Furthermore, the method was used to successfully isolate and identify a new set of heteroatom-containing aromatics (amines, ketones). The method is not intended to replace traditional sample preparation techniques or multi-dimensional chromatography but acts as a complementary tool. An in-depth comparison to routine characterization techniques is presented concerning advantages and disadvantages.