Unusual atmospheric pressure chemical ionization conditions for detection of organic peroxides

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 (≤50 °C) and probe temperature (70–200 °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 ( $\Delta H_{\rm reaction}^{\circ}$ ) 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. Copyright © 2003 John Wiley & Sons, Ltd.