Combination of ring type HPLC separation, ultrahigh-resolution mass spectrometry, and high field NMR for comprehensive characterization of crude oil compositions

Abstract

Abstract In this report, the combination of three analytical techniques, including high-performance liquid chromatography (HPLC) ring-type separation, two-dimensional nuclear magnetic resonance spectroscopy (2D NMR), and ultrahigh-resolution mass spectrometry (MS), for molecular-level characterization of crude oil was proposed and applied. The combination of data obtained using different techniques could be used to confirm and complement findings from each individual technique. The characteristics of each fraction obtained by three techniques agreed well and the aromaticity increased as the fraction number increased. In addition, based on the peak distribution in 2D NMR data and double bond equivalence (DBE) distribution obtained from high-resolution-MS, it was shown that the first to third fractions of HPLC ring-type separation contained HC class compounds with an aromatic ring core and multiple saturated cyclic rings. The structures and distribution of heteroatom class compounds could be also elucidated using the combined approach. S 1 class compounds were abundant in the first two fractions but S 2 class compounds were abundant in the second fraction which suggested that S 2 class compounds were more aromatic. Examining of DBE distribution provided further specific information by showing that compounds with thiophene (DBE = 3) and benzothiophene (DBE = 6) functional groups were abundant in the first fraction and ones with benzodithiophene (DBE = 8) in the second fraction. In contrast, a significant abundance of nonaromatic sulfur compounds were observed in the final polar fraction. We believe that this combined approach is essential to overcome the limitations of individual techniques and obtain further molecular-level information on complex crude oil samples.