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

Electron ionization mass spectra of the title compounds demonstrate intense peaks due to doubly charged ions. These ions have great analytical signifi cance 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 alpha cleavage reactions at the two substitute d exocyclic amino groups with prevailing methyl loss. The [M-2CH(3)](2+) io ns behave like characteristic ev en electron ions, either eliminating stabl e neutral molecules or undergoing Coulomb explosion into pairs of even elec tron ion products. Some of the products are characterized by proton transfe r to a neutral molecule having a high proton affinity, notably the formatio n of CH3NCH+ from [M-2CH(3)](2+) in simazine. Similar reactions have been r ecently observed for multiply protonated biomolecules. Kinetic energy relea ses and intercharge separations were determined for the Coulomb explosion r eactions of the [M-2CH(3)](2+) ions. (C) 1999 Elsevier Science B.V.