ANALYSIS OF ORGANOPHOSPHATE PESTICIDES BY A TROCHOIDAL ELECTRON MONOCHROMATOR MASS-SPECTROMETER SYSTEM

An electron monochromator mass spectrometer was used to study the reso nant electron energies versus negative ion masses of the organophospha te insecticides dicapthion, EPN, ethion, fenitrothion, leptophos, lept ophosoxon, paraoxon, and parathion. Each compound yielded a unique two -dimensional electron energy/mass spectrum. The most abundant ions are produced with electrons of energies between 0.03 and 1 eV, but ions r esult also from capture of electrons with energies ranging to 8.5 eV. Both resonance electron capture ions and dissociative electron capture ions are produced with electrons of energies ranging from 0.03 to 8.5 eV, and ions may have as many as three observable resonance state fro m which they are formed. Substituted thiophenoxide ions are postulated to arise by rearrangement of the parent thiophosphate ions through a spiro intermediate. Most fragment ions can be rationalized as arising through simple homolytic cleavage of the parent radical anions.