Effects of Solvents, Matrices, and of Reagents for Producing Adduct Ions on Liquid Ionization Mass Spectra of Monocyclic Hydrocarbon Hydroperoxides

Abstract

Mass spectra of hydroperoxides, such as cumen hydroperoxide (CHP), diisopropylbenzene hydroperoxide (DBH), p-mentane hydroperoxide (PMH) were investigated by liquid ionization (LPI) mass spectrometry. Hydrated molecular ions [M+H+nH₂O]⁺, n=1-10, were dominant in LPI mass spectra of all samples when they were dissolved simply in a solvent, although ethanol was a good solvent. When ethanol was used with butanol (1-3%), i.e., a mixed solvent, and/or with acetone, which was evaporated in the ionization chamber (as a vapor matrix), those hydrated ions were suppressed and [M+H]⁺ of PMH became the base peak. Acetone is a useful vapor matrix for obtaining [M+H]⁺. When pyridine (Py, 3-8%)-ethanol mixture was used as a solvent, molecular adduct ions [M+H+Py]⁺ became dominant for CHP and DBH. LPI-MS is useful not only for determining molecular weights of hydroperoxides but also for investigating the solvation and effects of various kinds of additives.