The first petroleum analysis with
electrospray ionization was demonstrated in 2000 by Zhan and
Fenn, who studied the polar species in petroleum distillates with low-resolution MS.[8] Electrospray ionization was coupled with high-resolution FT-ICR by
Marshall and coworkers.[1] To date, many studies on petroleomic analysis of crude oils have been published. Most work has been done by the group of Marshall at the
National High Magnetic Field Laboratory (NHMFL) and
Florida State University.[2]
Ionization methods
A high resolution FTICR mass spectrometer is often used for petroleomics.
Ionization of nonpolar petroleum components can be achieved by
field desorption ionization and
atmospheric pressure photoionization (APPI).[9] field desorption FT-ICR MS has enabled the identification of a large number of nonpolar components in crude oils that are not accessible by electrospray, such as
benzo- and
dibenzothiophenes,
furans,
cycloalkanes, and
polycyclic aromatic hydrocarbons (PAHs). A drawback of field desorption is that it is slow, mainly due to the need of ramping the current to the emitter in order to volatilize and ionize molecules. APPI can ionize both polar and nonpolar species,[10] and an APPI spectrum can be generated in just a few seconds. However, APPI ionizes a broad range of compound classes and produces both protonated and
molecular ion peaks, resulting in a complex mass spectrum.[2]
Kendrick analysis
Plot of Kendrick mass defect as function of Kendrick mass; horizontal lines indicate common repeat units. Each dot in the plot corresponds to a peak measured in a mass spectrum.
High mass resolution data analysis is usually undertaken by converting the mass spectra to the
Kendrick mass scale, in which the mass of a methylene unit is set to exactly 14 (CH2 = 14.0000 instead of 14.01565
daltons).[11] This rescaling of the data aids in the identification of homologous series according to alkylation, class (number of heteroatoms), and type (double bond equivalent, DBE, also called rings plus double bonds or degree of unsaturation). The scaled data is then used to obtain the Kendrick
mass defect (KMD), which is given by
where the nominal Kendrick is the Kendrick mass rounded to the nearest integer.
Double bond equivalent (DBE) is calculated according to
where C = number of carbons, H = number of hydrogens, X= number of halogens and N = number of nitrogens.[12] O
Compounds with the same DBE have the same mass defect. Therefore, Kendrick normalization yields a set of series with identical mass defect that appear as horizontal rows in a plot of DBE versus Kendrick mass. The data can also be plotted as a 3D heat-map to indicate the relative intensity of the mass spectral peaks. From the Kendrick plot, the species with peaks in the mass spectrum can be sorted into compound classes by the number of nitrogen, oxygen and sulfur heteroatoms.
^
abMarshall, Alan G.; Rodgers, Ryan P. (2004). "Petroleomics: The Next Grand Challenge for Chemical Analysis". Accounts of Chemical Research. 37 (1): 53–59.
doi:
10.1021/ar020177t.
ISSN0001-4842.
PMID14730994.
^Cho, Yunju; Ahmed, Arif; Islam, Annana; Kim, Sunghwan (2014). "Developments in FT-ICR MS instrumentation, ionization techniques, and data interpretation methods for petroleomics". Mass Spectrometry Reviews. 34 (2): 248–263.
Bibcode:
2015MSRv...34..248C.
doi:
10.1002/mas.21438.
ISSN0277-7037.
PMID24942384.
^Nadkarni, R. A. Kishore; Mendez, Aaron; Colin, Todd B. (2011). "Applications of Mass Spectrometry in the Petroleum and Petrochemical Industries". Spectroscopic Analysis of Petroleum Products and Lubricants: 287–287–62.
doi:
10.1520/MONO10113M.
ISBN978-0-8031-7020-9.
^Purcell, Jeremiah M.; Hendrickson, Christopher L.; Rodgers, Ryan P.; Marshall, Alan G. (2006). "Atmospheric Pressure Photoionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry for Complex Mixture Analysis". Analytical Chemistry. 78 (16): 5906–5912.
doi:
10.1021/ac060754h.
ISSN0003-2700.
PMID16906739.
^Hughey, Christine A.; Hendrickson, Christopher L.; Rodgers, Ryan P.; Marshall, Alan G.; Qian, Kuangnan (2001). "Kendrick Mass Defect Spectrum: A Compact Visual Analysis for Ultrahigh-Resolution Broadband Mass Spectra". Analytical Chemistry. 73 (19): 4676–4681.
doi:
10.1021/ac010560w.
ISSN0003-2700.
PMID11605846.
^Wu, Zhigang; Rodgers, Ryan P.; Marshall, Alan G. (2004). "Two- and Three-Dimensional van Krevelen Diagrams: A Graphical Analysis Complementary to the Kendrick Mass Plot for Sorting Elemental Compositions of Complex Organic Mixtures Based on Ultrahigh-Resolution Broadband Fourier Transform Ion Cyclotron Resonance Mass Measurements". Analytical Chemistry. 76 (9): 2511–2516.
doi:
10.1021/ac0355449.
ISSN0003-2700.
PMID15117191.
External links
Look up petroleomics in Wiktionary, the free dictionary.