Fast atom bombardment

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Schematic of a fast atom bombardment ion source for a mass spectrometer. FAB Schematic.jpg
Schematic of a fast atom bombardment ion source for a mass spectrometer.

Fast atom bombardment (FAB) is an ionization technique used in mass spectrometry in which a beam of high energy atoms strikes a surface to create ions. [1] [2] [3] It was developed by Michael Barber at the University of Manchester in 1980. [4] When a beam of high energy ions is used instead of atoms (as in secondary ion mass spectrometry), the method is known as liquid secondary ion mass spectrometry (LSIMS). [5] [6] [7] In FAB and LSIMS, the material to be analyzed is mixed with a non-volatile chemical protection environment, called a matrix, and is bombarded under vacuum with a high energy (4000 to 10,000 electron volts) atomic beam. The atoms are typically from an inert gas such as argon or xenon. Common matrices include glycerol, thioglycerol, 3-nitrobenzyl alcohol (3-NBA), 18-crown-6 ether, 2-nitrophenyloctyl ether, sulfolane, diethanolamine, and triethanolamine. This technique is similar to secondary ion mass spectrometry and plasma desorption mass spectrometry.

Contents

Ionization mechanism

Schematic of the fast atom bombardment process. Fast atom bombardment diagram.png
Schematic of the fast atom bombardment process.

FAB is a relatively low fragmentation (soft) ionization technique and produces primarily intact protonated molecules denoted as [M + H]+ and deprotonated molecules such as [M - H]−. Radical cations can also be observed in a FAB spectrum in rare cases. FAB was designed as an improved version of SIMS that allowed for the primary beam to no longer cause damaging effects to the sample. The major difference between the two techniques is the difference in the nature of the primary beam used; ions vs atoms. [8] For LSIMS, Cesium, Cs+ ions make up the primary beam and for FAB the primary beam is made up of Xe or Ar atoms. [8] Xe atoms are used because they tend to be more sensitive than Argon atoms due to their larger masses and more momentum. For the molecules to be ionized by FAB, first the slow moving atoms (Xe or Ar) are ionized by colliding electrons. Those slow moving atoms are then ionized and accelerated to a certain potential where they develop into fast moving ions that become neutral in a dense cloud of excess natural gas atoms that make a flowing stream of high translational energy atoms. [8] Although the exact mechanism of how the samples are ionized have not been fully discovered, the nature of its ionization mechanism is similar to matrix-assisted laser desorption/ionization (MALDI) [9] [10] and chemical ionization. [11]

Matrices and sample introduction

As previously stated, in FAB the samples are mixed with a non-volatile environment (matrix) in order to be analyzed. FAB uses a liquid matrix that is mixed with the sample in order to provide a sample ion current that is sustained, reduces damages made to the sample by absorbing the impact of the primary beam, and keeps the sample molecules form aggregating. [8] The liquid matrix, like any other matrix, most importantly provides a medium that promotes sample ionization. The most widely accepted matrix for this type of ionization is glycerol. Choosing the appropriate matrix for the sample is crucial because the matrix can also influence the degree of fragmentation of the sample (analyte) ions. The sample can then be introduced to FAB analysis. The normal method of introducing the sample-matrix mixture is through an insertion probe. The sample-matrix mixture is loaded on a stainless steel sample target on the probe, which is then placed in the ion source via a vacuum lock. The alternative method of introducing the sample is by using a device called continuous flow fast atom bombardment (CF)-FAB.

Continuous flow fast atom bombardment

In continuous flow fast atom bombardment (CF-FAB), the sample is introduced into the mass spectrometer insertion probe through a small diameter capillary. [12] (CF)-FAB was developed to minimize the problem of poor detection sensitivity that is caused by an excess of the matrix background that results in a high matrix-to-sample ratio. [8] When a metal frit is used to disperse the liquid on the probe, the technique is known as frit FAB. [13] [14] Samples can be introduced by flow injection, microdialysis, or by coupling with liquid chromatography. [15] Flow rates are typically between 1 and 20 μL/min. [13] CF-FAB has a higher sensitivity compared to static FAB [16]

Applications

ThermoQuest AvantGarde MS with quadrupole detector and FAB/EI source. FAB MS.jpg
ThermoQuest AvantGarde MS with quadrupole detector and FAB/EI source.

The first example of the practical application of this FAB was the elucidation of the amino acid sequence of the oligopeptide efrapeptin D. This contained a variety of very unusual amino acid residues. [17] The sequence was shown to be: N-acetyl-L-pip-AIB-L-pip-AIB-AIB-L-leu-beta-ala-gly-AIB-AIB-L-pip-AIB-gly-L-leu-L-iva-AIB-X. PIP = pipecolic acid, AIB = alpha-amino-isobutyric acid, leu = leucine, iva = isovaline, gly = glycine. This is a potent inhibitor of mitochondrial ATPase activity. Another application of FAB includes its original use for the analysis of condensed-phase samples. FAB can be use for measurements of the molecular weight of samples below 5000 Da, as well as their structural characteristics. FAB can be paired with various mass spectrometers for data analysis, such as with a quadrupole mass analyzer, liquid chromatography–mass spectrometry, and more.

Inorganic analysis

In 1983 a paper was published describing the use of fast atom bombardment mass spectrometry (FAB-MS) to analyze isotopes of calcium. [18] Glycerol was not used; samples in aqueous solution were deposited on the sample target and dried prior to analysis. The technique was effectively secondary ion mass spectrometry using a neutral primary beam. This was a welcomed development for biomedical researchers studying the nutrition and metabolism of essential minerals but lacking access to inorganic mass spectrometry instrumentation such as thermal ionization mass spectrometry or inductively-coupled plasma mass spectrometry (ICP-MS). In contrast, FAB mass spectrometers were widely found in biomedical research institutions. Multiple laboratories adopted this technique, using FAB-MS to measure isotope ratios in isotope tracer studies of calcium, iron, magnesium and zinc. [19] The analysis of metals required minimal modification of the mass spectrometers, e.g.replacing the stainless steel sample targets with pure silver ones to eliminate background from ionization of stainless steel components. [20] Signal acquisition systems were sometimes modified to perform peak jumping instead of scanning and to do ion counting detection. [21] While satisfactory precision and accuracy were attained with FAB-MS, the technique was labor-intensive with a very low sample through-put rate due in part to the absence of auto-sampling options. [19] By the early 2000s this severe sampling rate limitation had motivated users of FAB-MS for mineral isotope analysis to switch to conventional inorganic mass spectrometers, usually ICP-MS which also exhibited improved affordability and isotope ratio analysis performance by that time.

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<span class="mw-page-title-main">Mass spectrometry</span> Analytical technique based on determining mass to charge ratio of ions

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

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<span class="mw-page-title-main">Electron ionization</span> Ionization technique

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

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Static secondary-ion mass spectrometry, or static SIMS is a secondary ion mass spectrometry technique for chemical analysis including elemental composition and chemical structure of the uppermost atomic or molecular layer of a solid which may be a metal, semiconductor or plastic with insignificant disturbance to its composition and structure. It is one of the two principal modes of operation of SIMS, which is the mass spectrometry of ionized particles emitted by a solid surface upon bombardment by energetic primary particles.

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">Desorption atmospheric pressure photoionization</span> Ambient ionization technique

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<span class="mw-page-title-main">Thermal ionization mass spectrometry</span>

Thermal ionization mass spectrometry (TIMS) is also known as surface ionization and is a highly sensitive isotope mass spectrometry characterization technique. The isotopic ratios of radionuclides are used to get an accurate measurement for the elemental analysis of a sample. Singly charged ions of the sample are formed by the thermal ionization effect. A chemically purified liquid sample is placed on a metal filament which is then heated to evaporate the solvent. The removal of an electron from the purified sample is consequently achieved by heating the filament enough to release an electron, which then ionizes the atoms of the sample. TIMS utilizes a magnetic sector mass analyzer to separate the ions based on their mass to charge ratio. The ions gain velocity by an electrical potential gradient and are focused into a beam by electrostatic lenses. The ion beam then passes through the magnetic field of the electromagnet where it is partitioned into separate ion beams based on the ion's mass/charge ratio. These mass-resolved beams are directed into a detector where it is converted into voltage. The voltage detected is then used to calculate the isotopic ratio.

<span class="mw-page-title-main">Michael Barber (chemist)</span> British chemist and mass spectrometrist

Michael (Mickey) Barber, FRS was a British chemist and mass spectrometrist, best known for his invention of fast atom bombardment ionisation.

<span class="mw-page-title-main">Resonance ionization</span> Process to excite an atom beyond its ionization potential to form an ion

Resonance ionization is a process in optical physics used to excite a specific atom beyond its ionization potential to form an ion using a beam of photons irradiated from a pulsed laser light. In resonance ionization, the absorption or emission properties of the emitted photons are not considered, rather only the resulting excited ions are mass-selected, detected and measured. Depending on the laser light source used, one electron can be removed from each atom so that resonance ionization produces an efficient selectivity in two ways: elemental selectivity in ionization and isotopic selectivity in measurement.

In mass spectrometry, a matrix is a compound that promotes the formation of ions. Matrix compounds are used in matrix-assisted laser desorption/ionization (MALDI), matrix-assisted ionization (MAI), and fast atom bombardment (FAB).

References

  1. ↑ Morris HR, Panico M, Barber M, Bordoli RS, Sedgwick RD, Tyler A (1981). "Fast atom bombardment: a new mass spectrometric method for peptide sequence analysis". Biochem. Biophys. Res. Commun. 101 (2): 623–31. doi:10.1016/0006-291X(81)91304-8. PMID   7306100.
  2. ↑ Barber, Michael; Bordoli, Robert S.; Elliott, Gerard J.; Sedgwick, R. Donald; Tyler, Andrew N. (1982). "Fast Atom Bombardment Mass Spectrometry". Analytical Chemistry. 54 (4): 645A–657A. doi:10.1021/ac00241a817. ISSN   0003-2700.
  3. ↑ Barber M, Bordoli RS, Sedgewick RD, Tyler AN (1981). "Fast atom bombardment of solids (F.A.B.): a new ion source for mass spectrometry". Journal of the Chemical Society, Chemical Communications (7): 325–7. doi:10.1039/C39810000325.
  4. ↑ Barber, M.; Bordoli, R. S.; Sedgwick, R. D.; Tyler, A. N. (September 1981). "Fast atom bombardment of solids as an ion source in mass spectrometry". Nature. 293 (5830): 270–275. doi:10.1038/293270a0. ISSN   0028-0836.
  5. ↑ Stoll, R.G.; Harvan, D.J.; Hass, J.R. (1984). "Liquid secondary ion mass spectrometry with a focussed primary ion source". International Journal of Mass Spectrometry and Ion Processes. 61 (1): 71–79. Bibcode:1984IJMSI..61...71S. doi:10.1016/0168-1176(84)85118-6. ISSN   0168-1176.
  6. ↑ Dominic M. Desiderio (14 November 1990). Mass Spectrometry of Peptides. CRC Press. pp. 174–. ISBN   978-0-8493-6293-4.
  7. ↑ De Pauw, E.; Agnello, A.; Derwa, F. (1991). "Liquid matrices for liquid secondary ion mass spectrometry-fast atom bombardment: An update". Mass Spectrometry Reviews. 10 (4): 283–301. Bibcode:1991MSRv...10..283D. doi:10.1002/mas.1280100402. ISSN   0277-7037.
  8. 1 2 3 4 5 Chhabil., Dass (2007-01-01). Fundamentals of contemporary mass spectrometry. Wiley-Interscience. ISBN   9780471682295. OCLC   609942304.
  9. ↑ Pachuta, Steven J.; Cooks, R. G. (1987). "Mechanisms in molecular SIMS". Chemical Reviews. 87 (3): 647–669. doi:10.1021/cr00079a009. ISSN   0009-2665.
  10. ↑ Tomer KB (1989). "The development of fast atom bombardment combined with tandem mass spectrometry for the determination of biomolecules". Mass Spectrometry Reviews . 8 (6): 445–82. Bibcode:1989MSRv....8..445T. doi:10.1002/mas.1280080602.
  11. ↑ Székely, Gabriella; Allison, John (1997). "If the ionization mechanism in fast-atom bombardment involves ion/molecule reactions, what are the reagent ions? The time dependence of fast-atom bombardment mass spectra and parallels to chemical ionization". Journal of the American Society for Mass Spectrometry . 8 (4): 337–351. doi:10.1016/S1044-0305(97)00003-2. ISSN   1044-0305.
  12. ↑ Caprioli, Richard M. (1990). "Continuous-flow fast atom bombardment mass spectrometry". Analytical Chemistry. 62 (8): 477A–485A. doi:10.1021/ac00207a715. ISSN   0003-2700. PMID   2190496.
  13. 1 2 Jürgen H Gross (14 February 2011). Mass Spectrometry: A Textbook. Vol. 58. Springer Science & Business Media. pp. 494–. Bibcode:2005PhT....58f..59G. doi:10.1063/1.1996478. ISBN   978-3-642-10709-2.{{cite book}}: |journal= ignored (help)
  14. ↑ Caprioli, R. M. (1990). Continuous-flow fast atom bombardment mass spectrometry. New York: Wiley. ISBN   978-0-471-92863-8.
  15. ↑ Abian, J. (1999). "The coupling of gas and liquid chromatography with mass spectrometry". Journal of Mass Spectrometry. 34 (3): 157–168. Bibcode:1999JMSp...34..157A. doi: 10.1002/(SICI)1096-9888(199903)34:3<157::AID-JMS804>3.0.CO;2-4 . ISSN   1076-5174.
  16. ↑ Tomer, K. B.; Perkins, J. R.; Parker, C. E.; Deterding, L. J. (1991-12-01). "Coaxial continuous flow fast atom bombardment for higher-molecular-weight peptides: comparison with static fast atom bombardment and electrospray ionization". Biological Mass Spectrometry. 20 (12): 783–788. doi:10.1002/bms.1200201207. ISSN   1052-9306. PMID   1812988.
  17. ↑ Bullough, D.A., Jackson C.G., Henderson, P.J.F., Cottee, F.H., Beechey, R.B. and Linnett, P.E. Biochemistry International (1981) 4, 543-549
  18. ↑ Smith, David (December 1983). "Determination of Stable Isotopes of Calcium in Biological Fluids by Fast Atom Bombardment Mass Spectrometry". Analytical Chemistry. 55 (14): 2391–2393. doi:10.1021/ac00264a042.
  19. 1 2 Eagles, John; Mellon, Fred (1996). "Chapter 10: Fast Atom Bombardment Mass Spectrometry (FABMS)". In Mellon, Fred; Sandstrom, Britmarie (eds.). Stable Isotopes in Human Nutrition:Inorganic Nutrient Metabolism. London: Academic Press. pp. 73–80. ISBN   0-12-490540-4.
  20. ↑ Miller, Leland; Hambidge, Michael; Fennessey, Paul (1991). "Isotope Fractionation and Hydride Interference in Metal Isotope Analysis by Fast Atom Bombardment-Induced Secondary Ion Mass Spectrometry". Journal of Micronutrient Analysis. 8: 179–197.
  21. ↑ Krebs, Nancy; Miller, Leland; Naake, Vernon; Lei, Sian; Westcott, Jamie; Fennessey, Paul; Hambidge, Michael (June 1995). "The Use of Stable Isotope Techniques to Assess Zinc Metabolism". Nutritional Biochemistry. 6 (6): 292–301. doi:10.1016/0955-2863(95)00043-Y.
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