Petroleomics

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Petroleomics is the chemical characterization of petroleum such as this sample of North Sea crude oil. North Sea Oil IMG 0568 Kvitebjorn.JPG
Petroleomics is the chemical characterization of petroleum such as this sample of North Sea crude oil.

Petroleomics is the identification of the totality of the constituents of naturally occurring petroleum and crude oil using high resolution mass spectrometry. [1] [2] [3] In addition to mass determination, petroleomic analysis sorts the chemical compounds into heteroatom class (nitrogen, oxygen and sulfur), type (degree of unsaturation, and carbon number). [4] The name is a combination of petroleum and -omics (collective chemical characterization and quantification).

Contents

History

A gas chromatography-mass spectrometer at the National Bureau of Standards in 1948. SpectroscopyResearch 012.jpg
A gas chromatography-mass spectrometer at the National Bureau of Standards in 1948.

Mass spectrometry characterization of petroleum has been performed since the first commercial mass spectrometers were introduced in the 1940s. [5] [6] Early mass spectrometry was limited to relatively low molecular weight nonpolar species accessed mainly by electron ionization with mass analysis with sector mass spectrometers. By the end of the 20th century, separations combined with mass spectrometric techniques such as gas chromatography-mass spectrometry and liquid chromatography mass spectrometry have characterizated petroleum distillates such as gasoline, diesel, and gas oil. [7]

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. IonSpec FT-ICR (Fourier transform Ion cyclotron resonance) Mass spectrometer.jpg
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. Kendrick plot.gif
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.

The data can also be represented with a Van Krevelen diagram. [13]

See also

Related Research Articles

<span class="mw-page-title-main">Ion source</span> Device that creates charged atoms and molecules (ions)

An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.

<span class="mw-page-title-main">Electrospray ionization</span> Technique used in mass spectroscopy

Electrospray ionization (ESI) is a technique used in mass spectrometry to produce ions using an electrospray in which a high voltage is applied to a liquid to create an aerosol. It is especially useful in producing ions from macromolecules because it overcomes the propensity of these molecules to fragment when ionized. ESI is different from other ionization processes since it may produce multiple-charged ions, effectively extending the mass range of the analyser to accommodate the kDa-MDa orders of magnitude observed in proteins and their associated polypeptide fragments.

Fourier-transform ion cyclotron resonance mass spectrometry is a type of mass analyzer (or mass spectrometer) for determining the mass-to-charge ratio (m/z) of ions based on the cyclotron frequency of the ions in a fixed magnetic field. The ions are trapped in a Penning trap (a magnetic field with electric trapping plates), where they are excited (at their resonant cyclotron frequencies) to a larger cyclotron radius by an oscillating electric field orthogonal to the magnetic field. After the excitation field is removed, the ions are rotating at their cyclotron frequency in phase (as a "packet" of ions). These ions induce a charge (detected as an image current) on a pair of electrodes as the packets of ions pass close to them. The resulting signal is called a free induction decay (FID), transient or interferogram that consists of a superposition of sine waves. The useful signal is extracted from this data by performing a Fourier transform to give a mass spectrum.

<span class="mw-page-title-main">Matrix-assisted laser desorption/ionization</span> Ionization technique

In mass spectrometry, matrix-assisted laser desorption/ionization (MALDI) is an ionization technique that uses a laser energy-absorbing matrix to create ions from large molecules with minimal fragmentation. It has been applied to the analysis of biomolecules and various organic molecules, which tend to be fragile and fragment when ionized by more conventional ionization methods. It is similar in character to electrospray ionization (ESI) in that both techniques are relatively soft ways of obtaining ions of large molecules in the gas phase, though MALDI typically produces far fewer multi-charged ions.

<span class="mw-page-title-main">History of mass spectrometry</span>

The history of mass spectrometry has its roots in physical and chemical studies regarding the nature of matter. The study of gas discharges in the mid 19th century led to the discovery of anode and cathode rays, which turned out to be positive ions and electrons. Improved capabilities in the separation of these positive ions enabled the discovery of stable isotopes of the elements. The first such discovery was with the element neon, which was shown by mass spectrometry to have at least two stable isotopes: 20Ne and 22Ne. Mass spectrometers were used in the Manhattan Project for the separation of isotopes of uranium necessary to create the atomic bomb.

In mass spectrometry, direct analysis in real time (DART) is an ion source that produces electronically or vibronically excited-state species from gases such as helium, argon, or nitrogen that ionize atmospheric molecules or dopant molecules. The ions generated from atmospheric or dopant molecules undergo ion-molecule reactions with the sample molecules to produce analyte ions. Analytes with low ionization energy may be ionized directly. The DART ionization process can produce positive or negative ions depending on the potential applied to the exit electrode.

<span class="mw-page-title-main">Desorption electrospray ionization</span>

Desorption electrospray ionization (DESI) is an ambient ionization technique that can be coupled to mass spectrometry (MS) for chemical analysis of samples at atmospheric conditions. Coupled ionization sources-MS systems are popular in chemical analysis because the individual capabilities of various sources combined with different MS systems allow for chemical determinations of samples. DESI employs a fast-moving charged solvent stream, at an angle relative to the sample surface, to extract analytes from the surfaces and propel the secondary ions toward the mass analyzer. This tandem technique can be used to analyze forensics analyses, pharmaceuticals, plant tissues, fruits, intact biological tissues, enzyme-substrate complexes, metabolites and polymers. Therefore, DESI-MS may be applied in a wide variety of sectors including food and drug administration, pharmaceuticals, environmental monitoring, and biotechnology.

Sample preparation for mass spectrometry is used for the optimization of a sample for analysis in a mass spectrometer (MS). Each ionization method has certain factors that must be considered for that method to be successful, such as volume, concentration, sample phase, and composition of the analyte solution. Quite possibly the most important consideration in sample preparation is knowing what phase the sample must be in for analysis to be successful. In some cases the analyte itself must be purified before entering the ion source. In other situations, the matrix, or everything in the solution surrounding the analyte, is the most important factor to consider and adjust. Often, sample preparation itself for mass spectrometry can be avoided by coupling mass spectrometry to a chromatography method, or some other form of separation before entering the mass spectrometer. In some cases, the analyte itself must be adjusted so that analysis is possible, such as in protein mass spectrometry, where usually the protein of interest is cleaved into peptides before analysis, either by in-gel digestion or by proteolysis in solution.

<span class="mw-page-title-main">Laser spray ionization</span>

Laser spray ionization refers to one of several methods for creating ions using a laser interacting with a spray of neutral particles or ablating material to create a plume of charged particles. The ions thus formed can be separated by m/z with mass spectrometry. Laser spray is one of several ion sources that can be coupled with liquid chromatography-mass spectrometry for the detection of larger molecules.

<span class="mw-page-title-main">Matrix-assisted laser desorption electrospray ionization</span>

Matrix-assisted laser desorption electrospray ionization (MALDESI) was first introduced in 2006 as a novel ambient ionization technique which combines the benefits of electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI). An infrared (IR) or ultraviolet (UV) laser can be utilized in MALDESI to resonantly excite an endogenous or exogenous matrix. The term ‘matrix’ refers to any molecule that is present in large excess and absorbs the energy of the laser, thus facilitating desorption of analyte molecules. The original MALDESI design was implemented using common organic matrices, similar to those used in MALDI, along with a UV laser. The current MALDESI source employs endogenous water or a thin layer of exogenously deposited ice as the energy-absorbing matrix where O-H symmetric and asymmetric stretching bonds are resonantly excited by a mid-IR laser.

<span class="mw-page-title-main">Desorption atmospheric pressure photoionization</span>

Desorption atmospheric pressure photoionization (DAPPI) is an ambient ionization technique for mass spectrometry that uses hot solvent vapor for desorption in conjunction with photoionization. Ambient Ionization techniques allow for direct analysis of samples without pretreatment. The direct analysis technique, such as DAPPI, eliminates the extraction steps seen in most nontraditional samples. DAPPI can be used to analyze bulkier samples, such as, tablets, powders, resins, plants, and tissues. The first step of this technique utilizes a jet of hot solvent vapor. The hot jet thermally desorbs the sample from a surface. The vaporized sample is then ionized by the vacuum ultraviolet light and consequently sampled into a mass spectrometer. DAPPI can detect a range of both polar and non-polar compounds, but is most sensitive when analyzing neutral or non-polar compounds. This technique also offers a selective and soft ionization for highly conjugated compounds.

<span class="mw-page-title-main">Ambient ionization</span>

Ambient ionization is a form of ionization in which ions are formed in an ion source outside the mass spectrometer without sample preparation or separation. Ions can be formed by extraction into charged electrospray droplets, thermally desorbed and ionized by chemical ionization, or laser desorbed or ablated and post-ionized before they enter the mass spectrometer.

The Kendrick mass is defined by setting the mass of a chosen molecular fragment, typically CH2, to an integer value in amu (atomic mass units). It is different from the IUPAC definition, which is based on setting the mass of 12C isotope to exactly 12 amu. The Kendrick mass is often used to identify homologous compounds differing only by a number of base units in high resolution mass spectra. This definition of mass was first suggested in 1963 by chemist Edward Kendrick, and it has been adopted by scientists working in the area of high-resolution mass spectrometry, environmental analysis, proteomics, petroleomics, metabolomics, polymer analysis, etc.

<span class="mw-page-title-main">Laser ablation electrospray ionization</span>

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<span class="mw-page-title-main">Nanospray desorption electrospray ionization</span>

Nanospray desorption electrospray ionization (nano-DESI) is an ambient pressure ionization technique used in mass spectrometry (MS) for chemical analysis of organic molecules. In this technique, analytes are desorbed into a liquid bridge formed between two capillaries and the sampling surface. Unlike desorption electrospray ionization (DESI), from which nano-DESI is derived, nano-DESI makes use of a secondary capillary, which improves the sampling efficiency.

<span class="mw-page-title-main">Atmospheric pressure photoionization</span> Soft ionization method

Atmospheric pressure photoionization (APPI) is a soft ionization method used in mass spectrometry (MS) usually coupled to liquid chromatography (LC). Molecules are ionized using a vacuum ultraviolet (VUV) light source operating at atmospheric pressure, either by direct absorption followed by electron ejection or through ionization of a dopant molecule that leads to chemical ionization of target molecules. The sample is usually a solvent spray that is vaporized by nebulization and heat. The benefit of APPI is that it ionizes molecules across a broad range of polarity and is particularly useful for ionization of low polarity molecules for which other popular ionization methods such as electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are less suitable. It is also less prone to ion suppression and matrix effects compared to ESI and APCI and typically has a wide linear dynamic range. The application of APPI with LC/MS is commonly used for analysis of petroleum compounds, pesticides, steroids, and drug metabolites lacking polar functional groups and is being extensively deployed for ambient ionization particularly for explosives detection in security applications.

<span class="mw-page-title-main">Matrix-assisted ionization</span>

In mass spectrometry, matrix-assisted ionization is a low fragmentation (soft) ionization technique which involves the transfer of particles of the analyte and matrix sample from atmospheric pressure (AP) to the heated inlet tube connecting the AP region to the vacuum of the mass analyzer.

<span class="mw-page-title-main">Ron Heeren</span> Dutch mass spectrometry researcher

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Barbara Seliger Larsen is a mass spectrometrist, with a career in instrumentations and applications of mass spectrometry in industry, and served on the board of the American Society for Mass Spectrometry for several terms.

References

  1. 1 2 Marshall, 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. ISSN   0001-4842. PMID   14730994.
  2. 1 2 3 Marshall, A. G.; Rodgers, R. P. (2008). "Petroleomics: Chemistry of the underworld". Proceedings of the National Academy of Sciences. 105 (47): 18090–18095. Bibcode:2008PNAS..10518090M. doi: 10.1073/pnas.0805069105 . ISSN   0027-8424. PMC   2587575 . PMID   18836082.
  3. ↑ 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. ISSN   0277-7037. PMID   24942384.
  4. ↑ Oliver C. Mullins; Eric Y. Sheu; Ahmed Hammami; Alan G. Marshall (8 November 2007). Asphaltenes, Heavy Oils, and Petroleomics. Springer. ISBN   978-0-387-68903-6.
  5. ↑ Mynard Hamming (2 December 2012). Interpretation of Mass Spectra of Organic Compounds. Elsevier. pp. 3–. ISBN   978-0-323-14314-1.
  6. ↑ 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. ISBN   978-0-8031-7020-9.
  7. ↑ Rodgers, Ryan P.; McKenna, Amy M. (2011). "Petroleum Analysis". Analytical Chemistry. 83 (12): 4665–4687. doi:10.1021/ac201080e. ISSN   0003-2700. PMID   21528862.
  8. ↑ Zhan, Dongliang; Fenn, John B (2000). "Electrospray mass spectrometry of fossil fuels". International Journal of Mass Spectrometry. 194 (2–3): 197–208. Bibcode:2000IJMSp.194..197Z. doi:10.1016/S1387-3806(99)00186-4. ISSN   1387-3806.
  9. ↑ Hsu, Chang S.; Hendrickson, Christopher L.; Rodgers, Ryan P.; McKenna, Amy M.; Marshall, Alan G. (2011). "Petroleomics: advanced molecular probe for petroleum heavy ends". Journal of Mass Spectrometry. 46 (4): 337–343. Bibcode:2011JMSp...46..337H. doi: 10.1002/jms.1893 . ISSN   1076-5174. PMID   21438082.
  10. ↑ 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. ISSN   0003-2700. PMID   16906739.
  11. ↑ 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. ISSN   0003-2700. PMID   11605846.
  12. ↑ "1". Organic Structural Spectroscopy. Pearson Prentice Hall. 2011. ISBN   978-0-321-59256-9.
  13. ↑ 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. ISSN   0003-2700. PMID   15117191.
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