MARA): an Improved Method for Elemental Composition Assignment in Petroleomics
Total Page:16
File Type:pdf, Size:1020Kb
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by University of Debrecen Electronic Archive Subscriber access provided by UNIV OF LOUISIANA Article Mass-Remainder Analysis (MARA): An Improved Method for Elemental Composition Assignment in Petroleomics. Tibor Nagy, Ákos Kuki, Miklós Nagy, Miklos Zsuga, and Sándor Kéki Anal. Chem., Just Accepted Manuscript • Publication Date (Web): 26 Mar 2019 Downloaded from http://pubs.acs.org on March 30, 2019 Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts. is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties. Page 1 of 8 Analytical Chemistry 1 2 3 4 5 6 7 Mass-Remainder Analysis (MARA): An Improved Method for 8 Elemental Composition Assignment in Petroleomics. 9 10 Tibor Nagy, Ákos Kuki, Miklós Nagy, Miklós Zsuga, Sándor Kéki* 11 12 Department of Applied Chemistry, Faculty of Science and Technology, University of Debrecen, H-4032 Debrecen, Egyetem 13 tér 1., Hungary 14 ABSTRACT: Data processing and visualization methods have an important role in the mass spectrometric study of crude oils and 15 other natural samples. The recently invented data mining procedure: the Mass-remainder analysis (MARA), was further developed 16 for the use in petroleomics. MARA is based on the calculation of the remainder after dividing by the exact mass of a base unit, in 17 petroleomics by the mass of the CH2 group. The two key steps in the MARA algorithm are the separation of the monoisotopic 18 peaks from the other isotopic peaks and the subsequent intensity correction. The effectiveness of our MARA method was 19 demonstrated on the analysis of lubricating mineral oil and crude oil samples by ultra-high resolution Fourier transform ion 20 cyclotron resonance mass spectrometry (FT-ICR-MS) experiments. MARA is able to handle a huge portion of the overlapped peaks 21 even in a moderate resolution mass spectrum. Using MARA, effective chemical composition assignment and visual representation 22 were achieved for complex mass spectra recorded by a TOF analyzer with a limited resolution of 40 000 at m/z 400. In the absence of an ultra-high resolution mass analyzer, MARA can provide a closer look on the mass spectral peaks, like a digital zoom in a 23 simple camera. 24 25 26 + + 27 type (e.g. both the [C30H54OS + H] and [C30H57O3N3 + H] ions Introduction 28 have almost the same KMD values 0.120619 and 0.120468, 29 Crude oil is a very complex mixture of hydrocarbons and polar respectively). In order to differentiate between the above compositions, a better than 0.2 ppm mass accuracy is required at 30 organic compounds. As the world’s remaining oil reserves are becoming heavier and sourer, the knowledge of the molecular m/z 400. During the mass peak assignation, this issue can be 31 composition of crude oil is ever more important. The mass eliminated by pre-sorting the compounds according to their 32 spectrometric analysis of this extremely complex mixture may nominal mass (the mass peaks are divided into 14 nominal mass 33 require ultrahigh mass resolution and mass measurement accuracy series), as proposed by Hsu et al.24, however these coincidences 34 to separate the tens of thousands of individual compounds present are still interfering during the visualization and in the filtering 35 in crude oil. Fourier transform ion cyclotron resonance mass based on the KMD plots. Recently we have proposed a simple 36 spectrometry (FT-ICR-MS) has been successfully applied for algorithm, the Mass-remainder analysis (MARA) for the crude oil characterization.1-10. As alternatives, the performance of processing of complex copolymer mass spectra.26 MARA can not 37 “zig-zag” multi-reflecting time-of-flight (TOF) analyzer with only handle the issues mentioned above, but does not require a 38 ultrahigh resolving power,11 and Orbitrap Fourier transform mass multiple sorting algorithm. In this work, we demonstrate the 39 spectrometer were also used for petroleomic studies.12 ability of the Mass-remainder analysis for the elemental 40 Independently of analysers, fractionation of the sample is composition assignment and subsequent intensity correction by 41 beneficial, especially for non-polar compounds.13-15 The SARA the analysis of lubricating mineral oil and crude oil samples 42 (saturates, aromatics, resins, asphaltenes) fractionation is typical recorded FT-ICR-MS experiments. Moreover, owing to its for crude oil, and the collection of subfractions can increase the deisotoping procedure, MARA is expected to be able to analyze 43 number of assignations.16-19 Beside the identification of the the complex crude oil mass spectra recorded by a TOF analyzer 44 chemical composition, the structural analysis allows a better with moderate resolving power. With MARA, we report a new 45 understanding of crude oil behavior.20,21 Not only the high way for the data processing in petroleomics, and furthermore, to 46 resolution and mass accuracy, but also the data processing and the best of our knowledge, there have been no studies on the 47 visualization methods, such as Kendrick mass defect22 and van characterization of crude oil by a TOF analyzer with limited 23 48 Krevelen analyses have an important role in the study of crude resolution (40 000 at m/z 400). oils. Kendrick suggested a new mass scale, which converts the 49 mass of CH from 14.01565 to an integer value of 14. The Experimental 50 2 Kendrick mass defect (KMD) plot provides a tool for the sorting Chemicals. The crude oil sample is originated from Russia, 51 of compounds into homologous series. KMD plot simplifies the imported by the MOL group (Budapest, Hungary). LVO 100 1,2,24 52 identification of the mass peaks or enables the rapid lubricant oil (free of additives) was produced by Leybold (Vienna, 53 characterization of the sample by filtering characteristic Austria). Unused and used LVO 100 lubricants were measured. 25 54 compound classes. The compounds containing the same The used LVO 100 was applied in a rotary vacuum pump for 6 55 heteroatoms O, N and S (same class) and the number of rings plus months. Methanol (HPLC grade) and acetic acid (100%, double bonds (same type) but different numbers of CH groups 56 2 analytical reagent) were purchased from VWR International will have the same KMD values. Unfortunately, the Kendrick (Leuven, Belgium). Toluene was received from Sigma-Aldrich 57 mass defect calculations can generate coincidences, namely (Taufkirchen, Germany) and distilled before use. The samples 58 identical KMD values for the compounds of different class and/or 59 60 ACS Paragon Plus Environment Analytical Chemistry Page 2 of 8 were dissolved in toluene and completed with methanol. samples probably contain mass peak pairs m/z1 and m/z2 with m/z2 1 Concentration of the samples were 1.5 mg/mL, the solvent was - m/z1 = n R/round(R) + ε differences, where R = 14.01565, 2 toluene methanol mixture (V/V 4:1). 1 mL of the samples were round(R) = 14, n is an integer and ε (and ε' in Eq. 3) are small 3 spiked by 3 μL acetic acid and prepared freshly before each values. 4 measurement. For the comparison of FT-ICR and TOF measurements the concentration was 0.1 mg/mL. 5 Electrospray Quadrupole Time-of-Flight Mass 6 Spectrometry (ESI-QTOF MS). A Maxis II type Qq-TOF MS 7 instrument (Bruker Daltonik, Bremen, Germany) was used 8 equipped with an electrospray ion source where the spray voltage 9 was 4.5 kV. The resolution of the instrument is 40 000 at m/z 400 10 (FWHM), the mass accuracy is <600 ppb (internal calibration). N2 11 was utilized as drying (200°C, 4.0 L/min) and nebulizer gas (0.5 12 bar). The mass spectra were recorded by means of a digitizer at a sampling rate of 2 GHz. The spectra were calibrated in two steps, 13 externally by ESI tune mix (first step), from Bruker, and + 14 internally using [CnH2n-13N+H] (DBE = 8) well known series 15 appeared with high intensity (second step). The spectra were 16 evaluated with the Compass DataAnalysis 4.4 software from 17 Bruker. The sample solutions were introduced directly into the 18 ESI source with a syringe pump (Cole-Parmer Ins.