Laser spray ionization
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.
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 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.
A newer technique called laserspray ionization (LSI) without the space between laser and spray is so named to reflect the similarity with ESI using a matrix assisted laser desorption/ionization (MALDI) method. Laser ablation of a solid matrix/analyte mixture identical to those used in MALDI produces highly charged ESI-like ions. 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. Matrix-assisted ionization inlet (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 ionization inlet (LSII).
- Hiraoka, Kenzo (April 2004). "Laser spray: electric field-assisted matrix-assisted laser desorption/ionization". Journal of Mass Spectrometry. 39 (4): 341–50. doi:10.1002/jms.621. ISSN 1076-5174. PMID 15103647.
- Blakley, C; McAdams, M; Vestal, M (1978). "Crossed-beam liquid chromatoraph—mass spectrometer combination". Journal of Chromatography A. 158: 261. doi:10.1016/S0021-9673(00)89972-0.
- Murray, K. K.; D. H. Russell (1994). "Laser Spray Ionization for Biological Mass Spectrometry". American Laboratory. 26 (9): 38–44.
- 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 . PMID 19955086.
- 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.