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Laser spray ionization

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Schematic of LSI

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.

Types of laser spray ionization

Neutral spray

In one version of the laser spray interface, explosive vaporization and mist formation occur when an aqueous solution effusing from the tip of the stainless steel capillary is irradiated from the opposite side of the capillary by a 10.6 μm infrared laser. Weak ion signals could be detected when the plume was sampled through the ion sampling orifice. When a high voltage (3–4 kV) was applied to the stainless-steel capillary, strong ion signals appeared. The ion abundances were found to be orders of magnitude greater than those obtained by conventional electrospray ionization in the case of aqueous solutions. This approach to laser spray ionization is a hybrid of three basic techniques for the generation of gaseous ions from the condensed phase, i.e., energy-sudden activation, nebulization and the action of an electric field.

Laser spray mass spectrometry can faithfully reflect the solution-phase characteristics of biomolecules. It has been successfully applied to evaluate the binding affinities of protein-DNA.

Laser spray has better ionization efficiency than conventional electrospray ionization (ESI). In particular, the sensitivity became more than one order of magnitude higher in negative ion modes. It was also found that this technique has a potential benefit for the low concentration samples due to condensation effect of the formed droplet by the irradiation of laser. Higher the solvation energies of triply charged metal ions, stronger are the signals for ions.

Laserspray ionization

Laserspray Ionization (LSI) is a newer mass spectrometric technique commonly used with biomolecules, such as proteins. This method is similar to matrix-assisted laser desorption/ionization (MALDI) at atmospheric pressure in that it involves an analyte and matrix mixture. It also contains features from electrospray ionization, in which it produces a similar mass spectra. The mechanism was initially thought to involve laser induced production of highly charge matrix/analyte clusters that upon evaporation of the matrix produces ions by the same mechanism as ESI. LSI's ability to ablate proteins at atmospheric pressure in order to form a multiple of charged ions with a mass resolution of 100,000 when coupled with a quadrupole orbitrap mass spectrometer. The advantages of using LSI includes a solvent-free ionization technique, fast data acquisition, simply to use, and the improved fragmentation through multiple charging.

Laser spray inlet ionization

Main article: Inlet ionization
Schematic of LSII

Due to recent innovations to the laser spray technique, a new method of laser ablation using the spray method has surfaced. Laserspray inlet ionization (LSII) involves a matrix/analyte sample at atmospheric pressure being ablated, and the ionization process will take place in an ion transfer capillary tube located in the mass spectrometer inlet. The LSII method is also known as laserspray ionization vacuum (LSIV).

Applications

Matrix-assisted inlet ionization (MAII) has shown that the laser is not necessary for the ionization process. Ions are formed when matrix-analyte is introduced to the vacuum of a mass spectrometer through an inlet aperture. LSI is a subset of MAII and is now called laserspray inlet ionization (LSII). Laser spray inlet ionization and matrix-assisted inlet ionization can be coupled to a fourier transform ion cyclotron resonance (FT-ICR) mass analyzer to improve detection of peptides and proteins.

References

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  2. Blakley, C; McAdams, M; Vestal, M (1978). "Crossed-beam liquid chromatoraph—mass spectrometer combination". Journal of Chromatography A. 158: 261–276. doi:10.1016/S0021-9673(00)89972-0.
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  4. Trimpin, S.; Inutan, E. D.; Herath, T. N.; McEwen, C. N. (2009). "Laserspray Ionization, a New Atmospheric Pressure MALDI Method for Producing Highly Charged Gas-phase Ions of Peptides and Proteins Directly from Solid Solutions". Molecular & Cellular Proteomics. 9 (2): 362–7. doi:10.1074/mcp.M900527-MCP200. PMC 2830846. PMID 19955086.
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  6. Kojima, T.; Kudaka, I.; Sato, T.; Asakawa, T.; Akiyama, R.; Kawashima, Y.; Hiraoka, K. (1999-11-15). "Observation of triply charged metal ion clusters by electrospray and laser spray". Rapid Communications in Mass Spectrometry. 13 (21): 2090–2097. Bibcode:1999RCMS...13.2090K. doi:10.1002/(sici)1097-0231(19991115)13:21<2090::aid-rcm758>3.0.co;2-e. ISSN 1097-0231. PMID 10523765.
  7. Inutan, E. D.; Richards, A. L.; Wager-Miller, J.; Mackie, K.; McEwen, C. N.; Trimpin, S. (20 September 2010). "Laserspray Ionization, a New Method for Protein Analysis Directly from Tissue at Atmospheric Pressure with Ultrahigh Mass Resolution and Electron Transfer Dissociation". Molecular & Cellular Proteomics. 10 (2): M110.000760. doi:10.1074/mcp.M110.000760. PMC 3033668. PMID 20855542.
  8. Wang, Beixi; Lietz, Christopher B.; Inutan, Ellen D.; Leach, Samantha M.; Trimpin, Sarah (June 2011). "Producing Highly Charged Ions without Solvent Using Laserspray Ionization: A Total Solvent-Free Analysis Approach at Atmospheric Pressure". Analytical Chemistry. 83 (11): 4076–4084. doi:10.1021/ac2000576. PMID 21520968.
  9. Richards, A. L.; Lietz, C. B.; Wager-Miller, J.; Mackie, K.; Trimpin, S. (18 January 2012). "Localization and imaging of gangliosides in mouse brain tissue sections by laserspray ionization inlet". The Journal of Lipid Research. 53 (7): 1390–1398. doi:10.1194/jlr.D019711. PMC 3371251. PMID 22262808.
  10. Lutomski, Corinne A.; El-Baba, Tarick J.; Inutan, Ellen D.; Manly, Cory D.; Wager-Miller, James; Mackie, Ken; Trimpin, Sarah (July 2014). "Transmission Geometry Laserspray Ionization Using an Atmospheric Pressure Inlet". Analytical Chemistry. 86 (13): 6208–6213. doi:10.1021/ac501788p. PMC 4082395. PMID 24896880.
  11. McEwen C.N.; Pagnotti, V.S.; Inutan, E.D.; Trimpin, S. New Paradigm in Ionization: Multiply Charge Ion Formation from a Solid Matrix without a Laser or Voltage, Anal. Chem., 2010, 82, 9164-9168. Inutan, E.D.; Trimpin, S. Matrix Assisted Ionization Vacuum, a New Method for Biological Materials Analysis using Mass Spectrometry, Mol. and Cell Proteomics, 2013,12, 792-796.
  12. Nyadong, Inutan, Wang, Hendrickson, Trimpin, and Marshall (2013). "Laserspray and Matrix-Assisted Ionization Inlet Coupled to High-Field FT-ICR Mass Spectrometry for Peptide and Protein Analysis". American Society for Mass Spectrometry. 24 (3): 320–328. Bibcode:2013JASMS..24..320N. doi:10.1007/s13361-012-0545-1. PMID 23381687. S2CID 39268941.{{cite journal}}: CS1 maint: multiple names: authors list (link)
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