Nickel titanium

2014-01-22T13:48:13Z

92.74.237.245: /* Mechanism */ again

{{Disputed|date=April 2013}}

[[Image:Field desorption.gif|right|thumb|400 px|Schematic of field desorption ionization with emitter at left and [[mass spectrometer]] at right]]
'''Field desorption''' (FD)/field ionization (FI) refers to an [[ion source]] for [[mass spectrometry]] first reported by Beckey in 1969.<ref>Beckey H.D. ''Field ionization mass spectrometry.'' '''Research/Development''', ''1969'', 20(11), 26</ref> In field ionization, a high-potential electric field is applied to an ''emitter'' with a sharp surface, such as a razor blade, or more commonly, a filament from which tiny "whiskers" have formed. This results in a very high electric field which can result in ionization of gaseous molecules of the analyte. Mass spectra produced by FI have little or no fragmentation because FI is a soft [[ionization]] method. They are dominated by molecular radical cations M<sup>+.</sup> and less often, protonated molecules <math>[M+H]^+\,</math>.

==Mechanism==
In FD, the analyte is applied as a thin film directly to the emitter, or small crystals of solid materials are placed onto the emitter. Slow heating of the emitter then begins, by passing a high current through the emitter, which is maintained at a high potential (e.g. 5 kilovolts). As heating of the emitter continues, low-vapor-pressure materials get desorbed and ionized by alkali metal cation attachment.

==Applications==
Many earlier applications of FD/FI to analysis of polar and nonvolatile analytes such as polymers and biological molecules have largely been supplanted by newer ionization techniques. However, FD/FI remains one of the only ionization techniques that can produce simple mass spectra with molecular information from hydrocarbons and other particular analytes. The most commonly encountered application of FD/FI at the present time is the analysis of complex mixtures of hydrocarbons such as that found in petroleum fractions.

==Liquid injection==
The recently developed liquid injection FD ionization (LIFDI) <ref>HB Linden, Liquid injection field desorption ionization: a new tool for soft ionization of samples including air sensitive catalysts and non-polar hydrocarbons, Eur. J. Mass Spectrom. 2004, 10, 459-468</ref> technique "presents a major breakthrough for FD-MS of reactive analytes":<ref>JH Gross, Mass Spectrometry - A Textbook, Springer 2004, page 362</ref> Transition metal complexes are neutral and due to their reactivity, do not undergo protonation or ion attachment. They benefit from both: the '''soft''' FD ionization and the safe and simple LIFDI transfer of air/moisture sensitive analyte solution. This transfer occurs from the Schlenk flask to the FD emitter in the ion source through a fused silica capillary without breaking the vacuum.

== References ==
{{reflist}}

==Bibliography==
{{refbegin}}
* {{cite journal| last=Alexandrov | first=M. L. | coauthors=L. N. Gall, N. V. Krasnov, V. I. Nikolaev, V. A. Pavlenko, and V. A. Shkurov | year=1984 | title=Экстракция ионов из растворов при атмосферном давлении - Метод масс-спектрометрического анализа биоорганических веществ | trans_title=Extraction of ions from solutions at atmospheric pressure - A method for mass spectrometric analysis of bioorganic substances | journal=[[Doklady Akademii Nauk SSSR]] | volume=277 | issue=2 | pages=379–383 | language=Russian | url=http://md1.csa.com/partners/viewrecord.php?collection=TRD&recid=N8524706AH}}
*{{cite book |author=Prókai, László |title=Field desorption Mass Spectrometry |publisher=M. Dekker |location=New York |year=1990 |pages= |isbn=0-8247-8303-4 |oclc= |doi=}}
{{refend}}

[[Category:Ion source]]

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Nickel titanium