Mechanism of porphyrin reduction and decomposition in a high-pressure chemical ionization plasma

Journal Article · Wed Aug 02 04:00:00 EDT 1989 · Journal of the American Chemical Society; (USA)

DOI:https://doi.org/10.1021/ja00198a009· OSTI ID:7155559

Van Berkel, G J; Glish, G L; McLuckey, S A ^[1]; Tuinman, A A ^[2]

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1. Oak Ridge National Lab., TN (USA)
2. Univ. of Tennessee, Knoxville (USA)

Mechanisms for the in situ reduction and decomposition of porphyrins that occur in a high-pressure ammonia and hydrogen chemical ionization (CI) plasma are proposed based on studies of selected model porphyrins and porphyrinogens, both in a high-pressure Cl ion source and under low-pressure CI conditions in a three-dimensional quadrupole ion trap. Stepwise reduction of the porphyrin by radical hydrogen, aided by interaction of the porphyrin with the interior surfaces of the ion source, followed by ionization, forms molecular species, (M + nH){sup +}, where n = 0, 2, 4, and 6 when using hydrogen, and where n = 1,3,5, and 7 when using ammonia. The major fragment ions in the CI mass spectra, although arising from the reduced molecular species, are not products of simple unimolecular dissociation of the (M + nH){sup +} species. Mass spectrometry/mass spectrometry (MS/MS) studies show that the (M + nH){sup +} species, where n {>=} 2, fragment to form tri-, di-, and monopyrrolic units with masses two or more mass units less than the most abundant pyrrolic fragment ions observed in the CI mass spectra. Therefore, gas-phase unimolecular decomposition of the reduced ionic species can contribute somewhat to the overall CI mass spectrum. However, the major pyrrolic fragment ions observed in these spectra (as well as the majority of the other fragments) more likely result from unimolecular and thermal decomposition of the reduced species (both ionic and neutral) in the gas-phase and on the source surfaces, forming neutrals that possibly undergo additional reactions in the CI plasma prior to ionization.

• DOE Contract Number: AC05-84OR21400
• OSTI ID: 7155559
• Journal Information: Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 111:16; ISSN 0002-7863; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400500* -- Photochemistry
54 ENVIRONMENTAL SCIENCES
540100 -- Environment
Atmospheric-- (1990-)
AMMONIA
CARBOXYLIC ACIDS
CHEMICAL REACTIONS
DATA
DATA ANALYSIS
DECOMPOSITION
EXPERIMENTAL DATA
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HIGH PRESSURE
HYDRIDES
HYDROGEN COMPOUNDS
INFORMATION
IONIZATION
MASS SPECTROSCOPY
MEASURING INSTRUMENTS
MEASURING METHODS
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
NUMERICAL DATA
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PORPHYRINS
REDUCTION
SPECTROSCOPY