Analysis of Light Crude Oil Using Gas Chromatography High Resolution Time-of-Flight Mass Spectrometry

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1 nalysis of Light Crude Oil Using Gas Chromatography High Resolution Time-of-Flight ass pectrometry LECO Corporation; aint Joseph, ichigan U Keywords: GC, High Resolution, Time-of-Flight, Light Crude Oil 1. Introduction Crude oil is a very complex mixture of organic compounds including aliphatic, aromatic and heterocyclic compounds. nalysis of oil is complicated not only by the enormous number of multi-functional components, but also by the large variation in compound concentrations. 1,2 High performance timeof-flight mass spectrometry (TOF) is an ideal instrumental technique for the analysis of complex matrices such as crude oil. Fast acquisition rates, nonskewed data, broad mass analysis ranges and comprehensive detection using TOF greatly facilitate characterization of petroleum samples. Classification of oil components (e.g., saturates, aromatics, etc.) is simplified with the instrument s high resolving power and advanced software features. ulfur and nitrogen containing species that cause emission problems during combustion are of particular interest. These heteroatomic species can poison metal catalysts even at very low concentrations. Identification and robust characterization of these low-level materials can be very difficult because of the matrix effects associated with oil samples; however, high performance TOF with resolving powers up to 5, can help alleviate this problem. In this study, various light crude oil samples were analyzed for aromatic, polycyclic aromatic hydrocarbon and heterocyclic compounds. These compounds were characterized using a combination of elemental formula determinations with exact mass calculations and spectral library similarity searches. High performance TOF provided a comprehensive profile of samples and facilitated the search for these compounds in light crude oil. 2. Experimental Conditions amples Crude oil can be classified according to extraction location, density (light or heavy) and sulfur content (sweet or sour). amples analyzed in this study included rabian, Nigerian, asra and outh Louisiana Light crude oil standards. tandards (1 mg/ml in hexane) were diluted (5 μl 15 μl) and placed in vials for analysis. Experimental LECO Pegasus GC-HRT high resolution mass spectrometer was used for these analyses (Figure 1). It was equipped with an gilent Technologies 789 GC ystem and 7693 utosampler. Figure 1. LECO Pegasus GC-HRT with Folded Flight Path (FFP) Technology. t the heart of the Pegasus GC-HRT is its state of the art Folded Flight Path (FFP ) mass analyzer (Figure 2) which consists of a set of periodic lenses sandwiched between two gridless mirrors. Ions are introduced into the mass analyzer via orthogonal acceleration (), reflected through the analyzer and returned to a detector () located near the ion source. n onboard data acquisition system Kinetic lgorithmic ata cquisition ystem (K) allows for ultra-fast capture of high resolution spectra. Folded Flight Path of up to 4 m yields ultra-high resolution Vernchikov et.al. U Patent llows ultra-fast capture of high resolution spectra Figure 2. Pegasus GC-HRT FFP ass nalyzer. The Pegasus GC-HRT can be operated in three modes (Figure 3): Nominal ode (R = 1 at m/z = 219 FWH), High Resolution ode (R = 25, at m/z = ) and Ultra-High Resolution ode (R = 5, at m/z = ). GC and instrument parameters are listed below.

2 2.5e6 2.e6 1.5e6 1.e6 5.e5.e 1.e7 8.e6 6.e6 4.e6 2.e6.e ±.1 (12.933±.1Constant(2.)) (134.19±.1Constant(5.)) ( ±.1Constant( IC Nominal High Resolution Ultra-High Resolution 4.e7 irr 3.5e7 outh Louisiana Lens 3.e7 2.5e7 Nigerian irr 2.e7 L = 2m R = 1, L = 2m R = 25, L = 4m R = 5, 1.5e7 1.e7 5.e6 asra rabian Figure 3. LECO Pegasus GC-HRT Operating odes..e rabian Light IC 1 IC asra IC Nigerian 1 IC outh Louisiana Figure 4. ICs for outh Louisiana, Nigerian, asra and rabian light crude oil. GC Instrument: gilent 789 Column Type: Restek Rxi-5 (3 m x.25 mm x.25 μm) Injection: plit 25:1, 1 μl Inj. Temp.: 3 o C Oven: 4 o C (1 min) to 26 o C at 2.5 o C/min to 32 o C at 1 o C/min (5 min) Carrier Gas: He, 1. ml/min constant flow pectrometer: LECO Pegasus GC-HRT Ion ource: LECO EI Polarity: Positive (7 ev) Flight Path: High Resolution ode (R=25,) and Ultra-High Resolution ode (R=5,) cquisition: 6 spectra/second m/z Range: 5 58 High Resolution ode, 8 3 Ultra-High Resolution ode Calibration: PFT 3. Results The desired instrument characteristics for resolution of components and robust elemental composition assignments of compounds in petroleum include high mass resolving power and mass accuracy values below 1 ppm. 3 LECO s Pegasus GC-HRT meets these requirements but also provides a comprehensive sample profile coupled with high quality spectral data in a single acquisition. High resolution mode (L = 2m, R = 25,) analysis of crude light oil samples (outh Louisiana, Nigerian, asra and rabian) resulted in the analytical ion chromatograms (ICs) shown in Figure 4. This report will focus on the rabian and Nigerian oil samples. Paraffins (C 9 to C 28 ) in the rabian light sample are shown in Figure 5. n extracted ion chromatogram (XIC) with some substituted benzene molecules (C 8 H 1,, C 1 H 14,, C 12 H 18 ; RE = 4) in this sample is shown in Figure 6. 1.e7 8.e6 6.e6 4.e6 2.e6 n-c 9.e n-c1 n-c11 n-c112 High Resolution ode (L = 2 m; R = 25,) n-c13 n-c14 n-c15 n-c16 n-c17 n-c18 n-c19 n-c2 n-c21 n-c22 n-c IC Figure 5. IC showing paraffins in rabian light crude oil. C 8H 1 C 1 H 14 C 12 H 18 Figure 6. IC () and XIC () showing substituted benzene molecules in rabian light crude oil. Representative benzene compounds in the sample included: m-xylene, 1,2,4-trimethylbenzene, p- propyltoluene, 1,3-dimethyl-5-propylbenzene and 1,3,5-trimethyl-2-propylbenzene. ass spectral data for m-xylene and 1,2,4-trimethylbenzene are shown in Figures 7 and 8. ass accuracy values for the molecular ion and -CH 3 fragment of m-xylene were.27 and -1.1 ppm respectively. spectral similarity search of the (deconvoluted) mass spectrum for m-xylene against the NIT library yielded a similarity score of 979 out of a possible 1 points. ass accuracy values for the molecular ion and -CH 3 n-c24 n-25-28

3 - sample"rabian 1", enzene, 1,3-dimethyl-, at s Library Hit - Library: mainlib - enzene, 1,3-dimethyl sample"rabian 1", enzene, 1,2,4-trimethyl-, at s Library Hit - Library: mainlib - enzene, 1,2,4-trimethyl sample"rabian 1", enzene, 1-methyl-4-propyl-, at s Library Hit - Library: replib - enzene, 1-methyl-4-propyl sample"rabian 1", enzene, 1,3-dimethyl-5-(1-methylethyl)-, at s Library Hit - Library: mainlib - enzene, 1,3-dimethyl-5-(1-methylethyl) sample"rabian 1", enzene, 1,3,5-trimethyl-2-propyl-, at s Library Hit - Library: mainlib - enzene, 1,3,5-trimethyl-2-propyl e7 8.e6 6.e6 4.e6 2.e6.e 1.e7 8.e6 6.e6 4.e6 2.e6.e ± IC )) ± ± ± )) IC fragment of 1,2,4-trimethylbezene were 1.65 and.86 ppm. The spectral similarity score for this compound was 949/1. pectral data, mass accuracy values and spectral similarity scores for p-propyltoluene, 1,3-dimethyl- 5-propylbenzene and 1,3,5-trimethyl-2-propybenzene are displayed in Figure 9. C 1 H 8 + C 15 H 12 C 16H 14 C11H1 -CH 3 (-1.1ppm) (.27 ppm) C 8 H : (atch = 979/1) : NIT Figure 1. IC (C) and XICs ( and ) showing PHs in rabian light crude oil. Figure 7. () and NIT library () mass spectra for m-xylene. C 1 H 1 C 12 H 8 C 13 H 1 -CH 3 (.86ppm) (1.65 ppm) C 14 H : (949/1) : NIT Figure 11. IC () and XIC () showing sulfur heterocycles in rabian light crude oil. Figure 8. () and NIT library () mass spectra for 1,2,4-trimethylbenzene. Table 1. ass accuracy values for PHs in rabian light crude oil. (942/1) NIT (942/1) NIT (797/1) -C 2H 5 (.94ppm) -CH 3 (.83ppm) -C 2H 5 (.82ppm) (1.1 ppm) (.93 ppm) (-.2 ppm) C 1 H 14 Name Formula Calculated Ion m/z Observed Ion m/z ass elta (a) ass ccuracy (ppm) Naphthalene C1H ethylnaphthalene C11H ethylnaphthalene C11H ethylphenanthrene C15H ,3-imethylphenanthrene C16H Table 2. ass accuracy values for sulfur heterocycles in rabian light crude oil. Name Formula Calculated Ion m/z Observed Ion m/z ass elta (a) ass ccuracy (ppm) 3,5-imethylbenzo[b]thiophene C1H ibenzothiophene C12H ethyldibenzothiophene C13H ,7-imethyldibenzothiophene C14H NIT Figure 9. and NIT library mass spectra for p-propyltoluene (Top), 1,3-dimethyl- 5-propylbenzene (iddle) and 1,3,5-trimethyl-2-propylbenzene (ottom). The rabian light crude oil also contained a significant number of polyaromatic hydrocarbons (PHs) and heterocyclic sulfur compounds (Figures 1 and 11). The mass accuracy values for PHs and sulfur heterocycles ranged from -.72 to 1.3 ppm and.36 to 1.12 ppm respectively (Tables 1 and 2) C 12 H 18 Enhanced selectivity was observed when operating the Pegasus GC-HRT in ultra-high resolution mode. nalysis of the Nigerian light crude oil sample resulted in a clean extraction of over 5 alkyl substituted benzenes with formulas C 8 H 1,, C 1 H 14, and C 12 H 18 from the data (Figure 12). Excellent mass accuracy values were obtained for both molecular and fragment ions as shown for m-cymene (Figure 13). The average mass accuracy for the molecular ions and fragments of these compounds was.45 ppm (Table 3). PHs were also present in this sample (Figure 14). The average mass accuracy values for the PHs in rabian light crude oil was.5 ppm (Table 4).

4 2.5e5 2.e5 1.5e5 1.e5 5.e4.e ±.1 (12.933±.1Constant(2.)) (134.19±.1Constant(5.)) ( ±.1Constant(15.)) ( ±.1Constant(2.)) C 8 H 1 C 1H 14 C 12H 18 PH s (Figure 14), as well as, various naphthenes and heteroatomic compounds (Figure 15) were also present in the Nigerian sample. verage mass accuracy values for the PH s and heteroatomic species were.5 ppm and.91 ppm respectively (Tables 4 and 5). Figure 12. XIC of alkyl substituted benzene compounds in Nigerian light crude oil. 1.2e5 1.e5 8.e4 C 15 H 12 C 1 H 8 C 11 H 1 6.e4 4.e4 C 16 H 14 2.e4.e =.32 ppm ± ±.1 ( ±.25Constant(1.)) (26.19±.1Constant(1.)) = -.94ppm =.21 ppm Figure 14. PHs in Nigerian light crude oil sample Figure 13. mass spectrum of m-cymene in Nigerian light crude oil showing structures and mass accuracy values for parent and fragment ions. 4.5e4 4.e4 3.5e4 3.e4 2.5e4 2.e4 C 12 H 8 O 1.5e4 1.e4 5.e3 Table 3: ass accuracy values for substituted benzenes in Nigerian light crude oil. Formula R.T. (s) Quant asses Quant /N rea Observed Ion m/z ass ccuracy(ppm) C8H C8H C8H C9H C9H12-CH3 fragment ion C9H C9H C9H C9H C9H C9H C9H12-CH3 fragment ion C9H C9H12-CH3 fragment ion C1H C1H C9H12-CH3 fragment ion C1H C1H C1H C11H C1H C1H C1H C1H C1H C1H C1H C1H C1H C11H C11H C11H C11H C11H C11H16-C2H5 fragment ion C11H C11H C11H C11H C11H C11H C11H C11H C11H C11H C12H C12H C12H C12H C12H C12H C12H C12H C12H C12H C12H18-C3H7 fragment ion C12H C12H C11H16-C2H5 fragment ion C12H18-C3H7 fragment ion e Figure 15. Naphthenes and heteroatomic compounds in Nigerian light crude oil sample. Table 4. ass accuracy values for PHs in Nigerian light crude oil. Formula R.T. (s) Quant asses Quant /N rea Calculated Ion m/z Observed Ion m/z ass ccuracy(ppm) C1H C11H C11H C15H C15H C15H C15H C16H C16H C16H C16H C16H Table 5. ass accuracy values for Heteroatomic compounds in Nigerian light crude oil sample. Name Formula R.T. (s) Quant /Nrea Calculated Ion m/z Observed Ion m/z ass ccuracy(ppm) Naphthalene, C1H decahydro-, transtrans-4a-ethyl-decahydronaphthalene C11H ethyldecahydronaphthalene C11H ibenzofuran C12H8O Unknown C13H1O H-Xanthene C13H1O Unknown C13H1O ibenzothiophene C12H

5 4. Conclusions This study demonstrates the utility of high performance time-of-flight mass spectrometry for the comprehensive analysis of light crude oil samples. In addition to the increased resolution, the Pegasus GC-HRT provides the ability to acquire full mass range spectra without sacrificing sensitivity. This is beneficial for detecting not only target compounds (e.g., paraffins, aromatics, PHs, etc.), but also heteroatomic contaminants (e.g, dibenzothiophene, dibenzofuran, 9H-xanthene). aturated, aromatic, and heterocyclic compounds were identified using spectral similarity searches against existing nominal mass libraries together with highly accurate m/z parent and fragment ions for robust elemental formula determination. The Pegasus GC-HRT is an indispensable tool for the analysis of complex crude oil samples. 5. References 1 Liu P, hi Q, Chung KH, Zhang Y, Pan N, Zhao and Xu C, Energy Fuels 21, 24, peight, JG Handbook of Petroleum Product nalysis (Chemical nalysis: eries of onographs on nalytical Chemistry and Its pplications), John Wiley & ons. Chp. 1, pp (22). 3 hi Q, Hou, Chng KH, Xu C, Zhao and Zhang Y, Energy Fuels 21, 24, LECO Corporation 3 Lakeview venue t. Joseph, I 4985 Phone: Fax: info@leco.com IO-91:28 No. F 2445 LECO is a registered trademark of LECO Corporation. Form No /12-REV 212 LECO Corporation