IDENTIFICATION AND DETERMINATION OF FENITROTHION PHOTOLYSIS PRODUCTS IN WATER-METHANOL BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

The photodegradation of fenitrothion was examined in distilled water containing methanol. After 7 h of UV irradiation with a high-pressure mercury lamp, a fractionation step was carried out on a semi-preparative silica gel column. Eighty-eight fractions were collected by increasing the polarity of an eluent mixture of n-hexane-ethyl acetate (95 + 5) up to 100% ethyl acetate. Three more polar fractions in eluent mixtures of n-hexane-acetone (50 + 50), pure acetone and acetone-methanol (25 + 75) were obtained. The breakdown products formed were identified by gas chromatography-mass spectrometry with electron impact (EI) ionization. An estimate of the amount of fenitrothion degraded indicated that after 7 h Of irradiation, 10% of the parent compound still remained and different oxidation, isomerization and solvolysis products were produced. The P = S group was oxidized to give fenitrooxon and trimethyl phosphate in amounts of 0.1% and 3%, respectively. Carbomethoxyfenitrothion, due to oxidation followed by solvolysis, and the isomerization products O,O,S-trimethyl phosphorothioate and the S-methyl isomer of fenitrothion were obtained as photoalteration products at 10%, 10% and 3%, respectively. Other compounds corresponded to denitrofenitrothion, carbomethoxydenitrofenitrothion, parathion-methyl and 4-nitro-m-cresol at 0.2%, 0.4%, 0.4% and 0.4%, respectively. The EI mass spectra and the structures of the ions of the different fenitrothion photolysis products are given.