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.

Di‐n‐butyl sulfate (DNBS) has been studied by electrospray (ESI) and chemical (CI) ionization mass spectrometry. The use of methanol as solvent in electrospray ionization allows observation of relatively abundant [DNBS + CH3OH + H]+ ions (m/z 243) which upon collision dissociate to [DNBS + H]+ ions (m/z 211). In both ESI and CI experiments, it is found that [DNBS + H]+ ions lead to m/z 113 daughter ions. The composition of this m/z 113 fragment ion and its mechanism of formation have been established by high resolution measurements and CID‐MIKE experiments. An ‘internal substitution’ reaction involving an ion‐neutral intermediate is proposed to explain the formation of a [C8H17]+ ion (m/z 113) by loss of a H2SO4 molecule. Finally, a LC/ESI‐MS/MS quantification method is proposed in which a detection limit of di‐n‐butyl sulfate in the ppm range is obtained. It is suggested that the quantification method might be extended to higher dialkyl sulfates. Copyright © 2000 John Wiley & Sons, Ltd.