Editing Ion source (section)

==Ambient ionization==
{{Main|Ambient ionization}}
[[File:DART ion source capsule.jpg|thumb|300px|Direct analysis in real time ambient ionization ion source]]
In ambient ionization, ions are formed outside the mass spectrometer without sample preparation or separation.<ref name=Cooks2006>{{Cite journal | last1 = Cooks | first1 = R. Graham | last2 = Ouyang | first2 = Zheng | last3 = Takats | first3 = Zoltan | last4 = Wiseman | first4 = Justin M. | date = 2006 | title = Ambient Mass Spectrometry | journal = Science | volume = 311 | issue = 5767 | pages = 1566–70 | doi = 10.1126/science.1119426 | pmid = 16543450 | bibcode=2006Sci...311.1566C| s2cid = 98131681 }}</ref><ref name="MongeHarris2013">{{cite journal|last1=Monge|first1=María Eugenia|last2=Harris|first2=Glenn A.|last3=Dwivedi|first3=Prabha|last4=Fernández|first4=Facundo M.|title=Mass Spectrometry: Recent Advances in Direct Open Air Surface Sampling/Ionization|journal=Chemical Reviews|volume=113|issue=4|date=2013|pages=2269–2308|issn=0009-2665|doi=10.1021/cr300309q|pmid=23301684}}</ref><ref name="HuangYuan2010">{{cite journal|last1=Huang|first1=Min-Zong|last2=Yuan|first2=Cheng-Hui|last3=Cheng|first3=Sy-Chyi|last4=Cho|first4=Yi-Tzu|last5=Shiea|first5=Jentaie|title=Ambient Ionization Mass Spectrometry|journal=Annual Review of Analytical Chemistry|volume=3|issue=1|date=2010|pages=43–65|issn=1936-1327|doi=10.1146/annurev.anchem.111808.073702|pmid=20636033|bibcode=2010ARAC....3...43H}}</ref> Ions can be formed by extraction into charged electrospray droplets, thermally desorbed and ionized by [[chemical ionization]], or laser [[desorption|desorbed]] or [[Laser ablation|ablated]] and post-ionized before they enter the mass spectrometer.

Solid-liquid extraction based ambient ionization uses a charged spray to create a liquid film on the sample surface.<ref name="MongeHarris2013" /><ref name="Badu-TawiahEberlin2013">{{cite journal|last1=Badu-Tawiah|first1=Abraham K.|last2=Eberlin|first2=Livia S.|last3=Ouyang|first3=Zheng|last4=Cooks|first4=R. Graham|title=Chemical Aspects of the Extractive Methods of Ambient Ionization Mass Spectrometry|journal=Annual Review of Physical Chemistry|volume=64|issue=1|date=2013|pages=481–505|issn=0066-426X|doi=10.1146/annurev-physchem-040412-110026|pmid=23331308|bibcode = 2013ARPC...64..481B }}</ref> Molecules on the surface are extracted into the solvent. The action of the primary droplets hitting the surface produces secondary droplets that are the source of ions for the mass spectrometer. Desorption electrospray ionization (DESI) creates  charged droplets that are directed at a solid sample a few millimeters to a few centimeters away. The charged droplets pick up the sample through interaction with the surface and then form highly charged ions that can be sampled into a mass spectrometer.<ref name="pmid16237663">{{cite journal |vauthors=Takáts Z, Wiseman JM, Cooks RG |title=Ambient mass spectrometry using desorption electrospray ionization (DESI): instrumentation, mechanisms and applications in forensics, chemistry, and biology |journal=Journal of Mass Spectrometry |volume=40 |issue=10 |pages=1261–75 |date=2005 |pmid=16237663 |doi=10.1002/jms.922|bibcode = 2005JMSp...40.1261T |doi-access=free }}</ref>

Plasma-based ambient ionization is based on an electrical discharge in a flowing gas that produces metastable atoms and molecules and reactive ions. Heat is often used to assist in the desorption of volatile species from the sample. Ions are formed by chemical ionization in the gas phase. A [[DART ion source|direct analysis in real time (DART)]] source operates by exposing the sample to a dry gas stream (typically helium or nitrogen) that contains long-lived electronically or vibronically excited neutral atoms or molecules (or [[Metastability in molecules|"metastables"]]).  [[Excited state]]s are typically formed in the DART source by creating a glow discharge in a chamber through which the gas flows. A similar method called atmospheric solids analysis probe (ASAP) uses the heated gas from ESI or APCI probes to vaporize sample placed on a melting point tube inserted into an ESI/APCI source.<ref name="McEwen2005">{{cite journal |vauthors=McEwen CN, McKay RG, Larsen BS |title=Analysis of Solids, Liquids, and Biological Tissues Using Solids Probe Introduction at Atmospheric Pressure on Commercial LC/MS Instruments |journal=Anal. Chem. |volume=77 |issue=23 |pages=7826–7831 |date=2005 |doi=10.1021/ac051470k |pmid=16316194}}</ref>  Ionization is by APCI.

Laser-based ambient ionization is a two-step process in which a pulsed laser is used to desorb or ablate material from a sample and the plume of material interacts with an electrospray or plasma to create ions. Electrospray-assisted laser desorption/ionization (ELDI) uses a 337&nbsp;nm UV laser<ref name="pmid16299699">{{cite journal |vauthors=Shiea J, Huang MZ, Hsu HJ, Lee CY, Yuan CH, Beech I, Sunner J |title=Electrospray-assisted laser desorption/ionization mass spectrometry for direct ambient analysis of solids |journal=Rapid Commun. Mass Spectrom. |volume=19 |issue=24 |pages=3701–4 |date=2005 |pmid=16299699 |doi=10.1002/rcm.2243|bibcode=2005RCMS...19.3701S }}</ref> or 3&nbsp;μm infrared laser<ref name="Peng2010">{{cite journal|last1=Peng|first1=Ivory X.|last2=Ogorzalek Loo|first2=Rachel R.|last3=Margalith|first3=Eli|last4=Little|first4=Mark W.|last5=Loo|first5=Joseph A.|title=Electrospray-assisted laser desorption ionization mass spectrometry (ELDI-MS) with an infrared laser for characterizing peptides and proteins|journal=The Analyst|volume=135|issue=4|date=2010|pages=767–72|issn=0003-2654|doi=10.1039/b923303b|pmid=20349541|bibcode = 2010Ana...135..767P|pmc=3006438}}</ref> to  desorb material into an electrospray source. [[Matrix-assisted laser desorption electrospray ionization]] (MALDESI)<ref>{{cite journal | last1 = Sampson | first1 = JS | last2 = Hawkridge | first2 = AM | last3 = Muddiman | first3 = DC | year = 2006 | title = Generation and detection of multiply charged peptides and proteins by matrix-assisted laser desorption electrospray ionization (MALDESI) Fourier transform ion cyclotron resonance mass spectrometry | journal = J. Am. Soc. Mass Spectrom. | volume = 17 | issue = 12| pages = 1712–6 | doi = 10.1016/j.jasms.2006.08.003 | pmid = 16952462 | doi-access = free | bibcode = 2006JASMS..17.1712S }}</ref> is an atmospheric pressure ionization source for generation of multiply charged ions. An ultraviolet or infrared laser is directed onto a solid or liquid sample containing the analyte of interest and matrix desorbing neutral analyte molecules that are ionized by interaction with electrosprayed solvent droplets generating multiply charged ions. [[Laser ablation electrospray ionization]] (LAESI) is an ambient ionization method for mass spectrometry that combines laser ablation from a mid-infrared (mid-IR) laser with a secondary [[electrospray ionization]] (ESI) process.