title: Unusual atmospheric pressure chemical ionization conditions for detection of organic peroxides.
abstract: Organic peroxides such as the cumene hydroperoxide I (M(r) = 152 u), the di-tert-butyl peroxide II (M(r) = 146 u) and the tert-butyl peroxybenzoate III (M(r) = 194 u) were analyzed by atmospheric pressure chemical ionization mass spectrometry using a water-methanol mixture as solvent with a low flow-rate of mobile phase and unusual conditions of the source temperature (< or =50 degrees C) and probe temperature (70-200 degrees C). The mass spectra of these compounds show the formation of (i) an [M + H](+) ion (m/z 153) for the hydroperoxide I, (ii) a stable adduct [M + CH(3)OH(2)](+) ion (m/z 179) for the dialkyl peroxide II and (iii) several protonated adduct species such as protonated molecules (m/z 195) and different protonated adduct ions (m/z 227, 389 and 421) for the peroxyester III. Tandem mass spectrometric experiments, exact mass measurements and theoretical calculations were performed for characterize these gas-phase ionic species. Using the double-well energy potential model illustrating a gas-phase bimolecular reaction, three important factors are taken into account to propose a qualitative interpretation of peroxide behavior toward the CH(3)OH(2) (+), i.e. thermochemical parameters (DeltaHdegrees(reaction)) and two kinetic factors such as the capture constant of the initial stable ion-dipole and the magnitude of the rate constant of proton transfer reaction into the loose proton bond cluster.
mesh_terms: D001274:Atmospheric Pressure; D001555:Benzene Derivatives / Q000032:analysis / Q000737:chemistry; D005740:Gases / Q000737:chemistry; D006861:Hydrogen Peroxide / Q000032:analysis* / Q000737:chemistry; D007700:Kinetics; D013058:Mass Spectrometry / Q000379:methods*; D008958:Models, Molecular; D015394:Molecular Structure; D011522:Protons
chemical_list: D001555:Benzene Derivatives; D005740:Gases; D011522:Protons; D006861:Hydrogen Peroxide; C007164:cumene hydroperoxide