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Application of FT-ICR MS Equipped with Quadrupole Detection for Analysis of Crude Oil Eunji Cho, Matthias Witt, Manhoi Hur, Maeng-Joon Jung, and Sunghwan Kim Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b02644 • Publication Date (Web): 25 Oct 2017 Downloaded from http://pubs.acs.org on October 25, 2017
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Analytical Chemistry
Application of FTFT-ICR MS Equipped with Quadrupole Detection for Analysis of Crude Oil Eunji Cho1, Matthias Witt2, Manhoi Hur3,4, Maeng-Joon Jung1, Sunghwan Kim1,5* 1
Department of Chemistry, Kyungpook National University, 80 Daehak-ro, Buk-gu, Daegu 41566, Republic of Korea Bruker Daltonik GmbH, Fahrenheitrasse 4, 28359 Bremen, Germany 3 Department of Genetics, Development, and Cell Biology, Iowa State University, Ames, Iowa 50011, United States 4 Center for Metabolic Biology, Iowa State University, Ames, Iowa 50011, United States 5 Green-Nano Materials Research Center, Daegu 41566, Republic of Korea 2
ABSTRACT: Resolving power is a critical factor determining the quality of ultrahigh-resolving power mass spectra of crude oil. In this study, 7T Fourier-transform ion cyclotron mass spectrometry (FT-ICR MS), equipped with quadrupole detection, was applied and evaluated for crude oil analysis for the first time. Four spectra were obtained from two oil samples using two ionization methods. Resolving power of 1,500,000 was observed at m/z 400 with 4 seconds transient signal. Comparison with literature reports revealed that the achieved resolving power was comparable with or superior to those obtained from instruments using higher magnetic fields but without quadrupole detection. 6,000–10,000 peaks with an S/N ratio of 3 or higher were observed from the obtained spectra and over 97% of the peaks could be assigned to appropriate chemical formulas with an error within 1 ppm. Double bond equivalents vs. carbon number plots generated from the obtained data agreed well with those previously reported without quadrupole detection. Mass accuracy values of the assigned elemental formulas were examined and the average root mean square error was calculated to be only 160 ppb. Low unassignment rate of the observed peaks and strong agreement with previously reported results suggests that unwanted harmonics of reduced frequency are not significant for the data obtained with quadrupole detection. Overall, the data presented in this study show that FT-ICR MS equipped with quadrupole detection can be powerful a tool to examine complex mixtures like crude oil. To the best of our knowledge, this is the first paper reporting application of FT-ICR MS equipped with quadrupole detection for the oil analysis.
Introduction While finding new energy sources has been actively pursued, practical alternatives to conventional fossil fuels have not yet become available and the use of crude oil is still very important worldwide. However, as oil reserves become progressively heavier and demand for oil increases exponentially, technical developments that improve efficiency of the conversion of heavy oils to gasoline or diesel are necessary. One of the necessary areas of technical development is the identification of crude oil components at the molecular level. The obtained information on chemicals can then be utilized to understand and predict the properties and reactivity of crude oils.1-3 High-resolving power mass spectrometry, represented by Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), is an important tool to characterize chemicals in crude oils at the molecular level. Since crude oil is composed of hundreds of thousands of compounds, FT-ICR MS is the only analytical tool that can cope with its complexity.4,5 To improve the mass resolving power of FT-ICR MS further, technical developments including a new analytical cell and absorption-mode data processing have recently been developed. Both techniques were successfully applied to study chemical compositions of crude oils.6-11 Quadrupole detection is another technique developed to improve the resolving power of FT-ICR MS.12-14 Theoretical backgrounds for the quadrupole detection have previously been reported in the scientific literature.15,16 In the conventional detection method for FT-ICR MS, two cellular electrodes are used for detection. However, in quadrupole detection, four electrodes are used in the FT-ICR cell. As a result, peaks of frequency twice the cyclotron resonance frequency can be
observed, which consequently doubles the resolving power for a given magnetic field.17,18 Therefore, the improved resolving power provided by quadrupole detection can be proven for the FT-ICR MS analysis of crude oil. Despite its potential, the application of quadrupole detection for FT-ICR MS analysis on crude oil has not previously been reported. In this study, 7T FT- ICR MS quadrupole detection was applied to crude oil analysis for the first time. The obtained results were examined to evaluate the effectiveness of this technique for the analysis of complex mixtures. Experimental Materials and Sample preparation Two crude oil samples obtained from Saudi Arabia and Iraq were used in this study. The properties of the oils, such as sulfur and nitrogen contents, total acid number (TAN), and API numbers are provided in Table S-1. HPLC-grade toluene was purchased from Burdick & Jackson (Honeywell, Ulsan, Republic of Korea). The 2 samples were prepared to a final concentration of 1 mg/mL in 50:50 toluene/methanol. Mass spectrometry Positive-mode atmospheric-pressure photoionization (APPI) mass spectra were obtained using 7T FT-ICR MS (Solarix 2XR, Bruker Daltonics, GmbH, Bremen, Germany). The 7T FT-ICR MS was equipped with electronics and a cell that enabled the quadupolar detection. A gas-tight syringe (Hamilton Co., Reno, NV) and syringe pump were used to directly inject the sample at a flow rate of 600 µL/h. About 300 transients were obtained and co-added. Ion source parameters were op-
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