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Molecular Characterization of Volatiles and Petrochemical Base Oils by Photo-Ionization GC×GC-TOF-MS Anupam Giri, Marion Coutriade, Amandine Racaud, Koji Okuda, A. John Dane, Robert Bernard Cody, and Jean-François Focant Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.7b00124 • Publication Date (Web): 14 Apr 2017 Downloaded from http://pubs.acs.org on April 16, 2017
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Analytical Chemistry
Molecular Characterization of Volatiles and Petrochemical Base Oils by Photo-Ionization GC×GC-TOF-MS
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Authors:
Anupam Giri†, Marion Coutriade‡, Amandine Racaud‡, Koji Okuda§, John Dane§, Robert B. Cody§, Jean-François Focant*†
10 Afiliation:
†
University of Liège, Department of Chemistry, Organic & Biological Analytical Chemistry Group,
Allée du 6 aout, B6c, B-4000 Liège (Sart Tilman), Belgium 15
‡
Total Marketing Services, Centre de Recherche de Solaize, Chemin du Canal - BP 22, 69360 Solaize,
France §
Jeol USA, 11 Dearborn Road, Peabody, MA 01960, USA
*
To whom correspondance should be addressed:
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E-mail:
[email protected] Phone: +32 495 92 95 64 Fax: +32 4 366 43 87
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Analytical Chemistry
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ABSTRACT
The characterization of organic mixtures by comprehensive two-dimensional gas chromatography (GC×GC) coupled to electron impact (EI) ionization time-of-flight mass spectrometry 30
(TOF-MS) allows the detection of thousands of compounds. However, owing to the exhaustive fragmentation following EI ionization, despite the use of mass spectral libraries, a majority of the compounds remains unidentified because of the lack of parent ion preservation. Thus, soft-ionization energies leading to organic compounds being ionized with limited or no fragmentation, retaining the molecular ion, has been of interest for many years. In this study, photo-ionization (PI) was evaluated
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as the ion source for GC×GC-TOF-MS measurements. First, capabilities and limitations of PI were tested using an authentic mixture of compounds of several chemical classes. Ionization energy exhibited by PI, equivalent to 10.8 eV, resulted in significant retention of molecular ion information; [M]+. for alkanes, ketones, FAMEs, aromatics, [M-H]+. for chloroalkanes, and [M-H2O]+. for alcohols. Second, considering the potential of PI for hydrocarbons, base oils, complex mixtures of saturated and
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unsaturated hydrocarbons blended for finished lubricant formulations, were extensively evaluated. Several chemical classes of hydrocarbons were positively identified including a large number of isomeric compounds, both aliphatics and cyclics. Interestingly, branched-alkanes were ionized with lower excess internal energy, not only retaining the molecular ions but also exhibited unique fragmentation patterns. The results presented herein offer a unique perspective into the detailed
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molecular characterization of base oils. Such unprecedented identification power of PI coupled with GC×GC-TOF-MS is the first report covering volatiles to low-volatile organic mixtures.
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Analytical Chemistry
INTRODUCTION Since the invention of the concept 25 years ago,1 comprehensive two-dimensional gas 55
chromatography (GC×GC) has extensively been evaluated and adopted to develop methods to analyze complex samples, starting from volatile organic compounds (VOCs)2,3 to higher end unresolved complex middle distillates.4,5 In addition, time-of-flight mass spectrometric (TOF-MS) detection further facilitates the identification of compounds by providing adequate spectrum acquisition speed, producing robust structural information without mass spectral skewing across the chromatographic
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peak. Among the various ionization techniques used in GC-MS, electron ionization (EI) is the most common one and traditionally used at 70 eV, imparting a large amount of excess energy (most organic compounds have ionization potential
