Editing Ion source (section)

===Matrix-Assisted Ionization===
Matrix-Assisted Ionization (MAI) is similar to MALDI in sample preparation, but a laser is not required to convert analyte molecules included in a matrix compound into gas-phase ions.  In MAI, analyte ions have charge states similar to electrospray ionization but obtained from a solid matrix rather than a solvent.  No voltage or laser is required, but a laser can be used to obtain spatial resolution for imaging.  Matrix-analyte samples are ionized in the vacuum of a mass spectrometer and can be inserted into the vacuum through an atmospheric pressure inlet. Less volatile matrices such as 2,5-dihydroxybenzoic acid require a hot inlet tube to produce analyte ions by MAI, but more volatile matrices such as 3-nitrobenzonitrile require no heat, voltage, or laser.  Simply introducing the matrix-analyte sample to the inlet aperture of an atmospheric pressure ionization mass spectrometer produces abundant ions. Compounds at least as large as bovine serum albumin [66 kDa] can be ionized with this method.<ref name="Trimpin2013">{{cite journal |vauthors=Trimpin S, Wang B, Lietz CB, Marshall DD, Richards AL, Inutan ED |title=New Ionization Processes and Applications for Use in Mass Spectrometry |journal=Rev. Biochem. Mol. Biol. |year=2013 |volume=48 |issue=5 |pages=409–429|doi=10.3109/10409238.2013.806887 |pmid=23883414 }}</ref> In this method, the inlet to the mass spectrometer can be considered the ion source.