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Abstract
Hydrocarbons present in saturated fractions of crude oils can be assessed by atmospheric pressure chemical ionization (APCI) using small hydrocarbons as ionizing reagents in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). In this work, five paraffin standards of different average molar mass distributions (Mw) were easily ionized by APCI(+)FT-ICR MS using isooctane as the reagent gas. Data of Mw, carbon number and double bond equivalent (DBE) distributions corresponding to linear and cyclic hydrocarbons (HCs) were compared to results obtained from analysis of high temperature gas chromatography with a flame ionization detector (HTGC-FID), comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC×GC-MS) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. APCI(+)FT-ICR MS data showed good agreement with those of analytical techniques. Furthermore, the ability of APCI(+) to assess n-paraffin, even in blends with polyaromatic hydrocarbon molecules such as coronene (Mw = 301 Da) at concentrations from 2.5 to 25 µg mL-1, was demonstrated. The typical MS paraffin profile (containing repeating mass units of 14 Da) was clearly confirmed, being totally suppressed when a concentration of 25 µg mL-1 of coronene was used. This phenomenon was also evidenced in one of two saturated fractions produced using saturates, aromatics and polar (SAP) compound fractionation methodology.
Highlights
Data of molecular weights (Mws), carbon number (CN) and double bond equivalent (DBE) distributions corresponding to linear and cyclic HCs were compared to the results obtained by other analytical methods, such as high temperature gas chromatography with a flame ionization detector (HTGC‐FID), comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC×GC-MS) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy
The distribution of carbon number among paraffin samples were in good agreement with High-temperature gas chromatography (HTGC) data
The Hβ contents could be directly associated to Mws that increased in the following order: standard P1 (Mw = 431 Da) < standard P2 (Mw = 444 Da) < standard P4 (Mw = 551 Da) < standard P3 (Mw = 571 Da) < standard P5 (Mw = 662 Da)
Summary
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 (CcHhNnOoSs) and double bond equivalent (DBE),. The mechanism that best explains the ionization of linear HCs is hydride abstraction, i.e., the formation of [M – H]+ ions.[15] This study is a continuation of the earlier work published by our group,[16] where five paraffin standards of different average molar mass distribution (Mw) were ionized by APCI(+)FT-ICR MS using isooctane as the reagent gas. Data of Mw, carbon number (CN) and DBE distributions corresponding to linear and cyclic HCs were compared to the results obtained by other analytical methods, such as high temperature gas chromatography with a flame ionization detector (HTGC‐FID), comprehensive two-dimensional gas chromatography coupled to mass spectrometry (GC×GC-MS) and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. GC Image software (ZOEX Corporation, Houston, Texas, USA) was used for the identification of compounds
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