TY - JOUR
T1 - Oxidative Ionization Under Certain Negative-Ion Mass Spectrometric Conditions
AU - Hassan, Isra
AU - Pavlov, Julius
AU - Errabelli, Ramu
AU - Attygalle, Athula B.
N1 - Publisher Copyright:
© 2016, American Society for Mass Spectrometry.
PY - 2017/2/1
Y1 - 2017/2/1
N2 - 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. [Figure not available: see fulltext.]
AB - 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. [Figure not available: see fulltext.]
KW - APCI
KW - Ambient ionization
KW - ESI
KW - HePI
KW - Hydroquinone
KW - Oxidative ionization
KW - Thermometer ions
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U2 - 10.1007/s13361-016-1527-5
DO - 10.1007/s13361-016-1527-5
M3 - Article
C2 - 27822704
AN - SCOPUS:85009223201
SN - 1044-0305
VL - 28
SP - 270
EP - 277
JO - Journal of the American Society for Mass Spectrometry
JF - Journal of the American Society for Mass Spectrometry
IS - 2
ER -