NDLI: Oxidative Ionization Under Certain Negative-Ion Mass Spectrometric Conditions

Content Provider	Springer Nature Link
Author	Hassan, Isra Pavlov, Julius Errabelli, Ramu Attygalle, Athula B.
Copyright Year	2016
Abstract	1,4-Hydroquinone and several other phenolic compounds generate (M – 2) $^{–•}$ radical-anions, rather than deprotonated molecules, under certain negative-ion mass spectrometric conditions. In fact, spectra generated under helium-plasma ionization (HePI) conditions from 1,4-hydroquinone and 1,4-benzoquinone (by electron capture) were practically indistinguishable. Because this process involves a net loss of H$^{•}$ and H$^{+}$, it can be termed oxidative ionization. The superoxide radical-anion (O$_{2}$ $^{–•}$), known to be present in many atmospheric-pressure plasma ion sources operated in the negative mode, plays a critical role in the oxidative ionization process. The presence of a small peak at m/z 142 in the spectrum of 1,4-hydroquinone, but not in that of 1,4-benzoquinone, indicated that the initial step in the oxidative ionization process is the formation of an O$_{2}$ $^{–•}$ adduct. On the other hand, under bona fide electrospray ionization (ESI) conditions, 1,4-hydroquinone generates predominantly an (M – 1) $^{–}$ ion. It is known that at sufficiently high capillary voltages, corona discharges begin to occur even in an ESI source. At lower ESI capillary voltages, deprotonation predominates; as the capillary voltage is raised, the abundance of O$_{2}$ $^{–•}$ present in the plasma increases, and the source in turn increasingly behaves as a composite ESI/APCI source. While maintaining post-ionization ion activation to a minimum (to prevent fragmentation), and monitoring the relative intensities of the m/z 109 (due to deprotonation) and 108 (oxidative ionization) peaks recorded from 1,4-hydroquinone, a semiquantitative estimation of the APCI contribution to the overall ion-generation process can be obtained. Graphical Abstract ᅟ
Starting Page	270
Ending Page	277
Page Count	8
File Format	PDF
ISSN	10440305
Journal	Journal of The American Society for Mass Spectrometry
Volume Number	28
Issue Number	2
e-ISSN	18791123
Language	English
Publisher	Springer US
Publisher Date	2016-11-07
Publisher Institution	The American Society for Mass Spectrometry
Publisher Place	New York
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Oxidative ionization HePI APCI ESI Hydroquinone Thermometer ions Ambient ionization Analytical Chemistry Biotechnology Organic Chemistry Proteomics Bioinformatics
Content Type	Text
Resource Type	Article
Subject	Spectroscopy Structural Biology

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