Comprehensive Characterization of Asphaltenes by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry Precipitated under Different n-Alkanes Solvents

Abstract

Asphaltenes are still problematic fractions and their composition is not fully unveiled as it relates to the original crude oil and the precipitation method. In this work, the composition of asphaltenes precipitated with n-heptane and n-pentane from ten crude oils from the Sergipe-Alagoas Basin were assessed by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) using five ionization procedures (electrospray ionization (ESI), ESI(+) with formic acid, ESI(−) with ammonium hydroxide, and ESI(−) with tetramethylammonium hydroxide, and atmospheric pressure photoionization (APPI), APPI(+) and APPI(−)) in combination with a 7.2 T LTQ FT Ultra Thermo Fisher spectrometer. The purpose was to evaluate compositional differences between C5-and C7-asphaltenes according to the adopted ionization methodologies. Asphaltenes were compared as a function of heteroatomic composition and aromaticity. Chemometrics strategies were employed to evaluate the heteroatom classes of higher variation among the groups. Ions that were shared by the asphaltenes and the crude oils and between the ionization methods were also evaluated for similarity. Results showed that n-heptane asphaltenes are more aromatic than n-pentane asphaltenes, which in turn were found to be more acidic and to display a higher heteroatomic complexity. Principal component analysis and the evaluation of shared ions showed that APPI(±) is able to detected asphaltene ions directly from the whole crude oil. It was also found that the use of different ionization methods with and without additives is fundamental to obtain more comprehensive chemical profiles in terms of classes and their constituents for crude oils and their asphaltenes and that the specific n-alkane used to precipitate asphaltenes leads to different chemical profiles.

Modified SARA Method to Unravel the Complexity of Resin Fraction(s) in Crude Oil

“…The aromaticity of the detected compounds can be evaluated using the assigned molecular formulas and the corresponding mean DBE/C ratio, which provides a good measurement of the global aromaticity of the compound class. 26 The mean values of DBE/C were calculated using all of the molecular formulas assigned for the fractions with different ionization techniques, and the values are summarized in Table 2. There is no significant trend in the means of DBE/C when comparing the data for the same ionization technique among the samples.…”

APCI(+)FT-ICR MS Analysis of Hydrocarbons Using Isooctane as Ionizing Reagent - A Comparison with HTGC-FID, GC×GC-MS and NMR

“…Class, DBE distributions and CN versus DBE plots were constructed to allow the interpretation of the results. 1,3,4,13,17,25 For the CN versus DBE and DBE versus intensity plots, DBE was the number of rings added and the number of double bonds in each molecular structure. The unsaturation level of each compound can be deduced directly from its DBE value, according to equation 1:…”

“…Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides unsurpassed mass resolution and accuracy, enabling the complex composition of petroleum, [1][2][3] its cuts, 4 paraffin [4][5][6][7] and asphaltene fractions to be analyzed on a molecular level. 1,[8][9][10] Accurate mass measurements define the unique elemental composition (C c H h N n O o S s ) and double bond equivalent (DBE), facilitating material classification by heteroatom content and the degree of aromaticity. [11][12][13] Different methodologies have been proposed to improve the ionization of hydrocarbons (HCs) using mass spectrometry techniques.…”

“…Classification of hydrogen types present in the paraffin standards according to1 H NMR data. The confidence interval associated with the numerical data is shown in parentheses.…”

Optimization of Atmospheric Pressure Photoionization for the Crude Oil Analysis Using Ultra-High Resolution Mass Spectrometry

“…[9][10][11][12] ESI FT-ICR MS has, therefore, been widely used to determine sulfurcontaining species in heavy crude oil 13 and non-polar polyaromatic hydrocarbons and polyaromatic heterocycles in asphaltenes, 10,14 as well as to classify biodegraded and non-biodegraded crude oils focused on the O 2 -class. 12 Atmospheric pressure photoionization (APPI) has also been applied to crude oil analysis, [15][16][17] but much less intensively, most particularly when the goal is to efficiently ionize nonpolar sulfur species and polycyclic aromatic hydrocarbons, which are interesting classes because they affect the petroleum refinery and its regulation by governmental agencies. 18 The direct infusion of crude oil solutions on APPI can positively charge species to produce both radical cations (M +• ) and protonated molecules ([M + H] + ) 18 by APPI(+) acquisition mode or negatively to produce deprotonated molecules ([M -H] -) by APPI(-) acquisition mode.…”