Photocatalytic pilot scale degradation study of pyrimethanil and of its main degradation products in waters by means of solid-phase extraction followed by gas and liquid chromatography with mass spectrometry detection

Aqueous solutions of Pyrimethanil, as technical grade product (TP), with 98.2% purity, and commercial formulation (CF), containing 40% (w/v) of Pyrimethanil, were submitted to photocatalytic degradation under sunlight in the presence of TiO2 as catalyst in a preindustrial pilot plant. Complete Pyrimethanil degradation was achieved after ca. 230 min of irradiation, in both TP and CF, but total mineralization was not observed, as was demonstrated by the TOC values of 3-4 mg/L, measured at the end of the experiments (907 min). A qualitative and quantitative study of the degradation products (DPs) generated during the process was performed by GC-MS, using El and Cl as ionization modes, and by LC-API-MS, using Atmospheric Pressure Chemical Ionization (APCl) and Electrospray (ES) interfacing techniques. Up to 22 compounds could be detected as degradation intermediates. To evaluate the extraction efficiency of these DPs from the aqueous solution, specially for the more polar intermediates, a recovery study was performed with Pyrimethanil and seven of the commercially available DPs. Liquid-liquid extraction (LLE) and solid-phase extraction (SPE), with different sorbents, were compared. A SPE method using Lichrolut-EN cartridges was selected as the most adequate, but recoveries less than or equal to 60% were obtained for four of the DPs studied (aniline, formamide, 1,3-benzenediol, and 4,6-dimethyl-2-pyrimidinamine). Structure identification of DPs allowed us to propose two main routes in the degradation process. One route involves the attack of hydroxyl radicals to the pyrimidine and benzene rings with further rings opening and the other one corresponds to a photoinduced hydrolysis of the molecule by the amine group bonds.