Doubly charged ions in the electron ionization mass spectra of 4,6-di(substituted)amino s-triazines

Abstract

Electron ionization mass spectra of the title compounds demonstrate intense peaks due to doubly charged ions. These ions have great analytical significance for the screening of these herbicides. The ions [M–2CH 3] 2+ reach 25%–30% of the base peak at 70 eV. The origin of these ions and their modes of fragmentation were studied through high voltage scans and mass analyzed ion kinetic energy spectroscopy on a reverse geometry double focusing mass spectrometer. The doubly charged parent ions of the title compounds behave like diradicals and undergo α cleavage reactions at the two substituted exocyclic amino groups with prevailing methyl loss. The [M–2CH 3] 2+ ions behave like characteristic even electron ions, either eliminating stable neutral molecules or undergoing Coulomb explosion into pairs of even electron ion products. Some of the products are characterized by proton transfer to a neutral molecule having a high proton affinity, notably the formation of CH 3NCH + from [M–2CH 3] 2+ in simazine. Similar reactions have been recently observed for multiply protonated biomolecules. Kinetic energy releases and intercharge separations were determined for the Coulomb explosion reactions of the [M–2CH 3] 2+ ions.