STABILITY OF ORGANOPHOSPHORUS PESTICIDES ON DISPOSABLE SOLID-PHASE EXTRACTION PRECOLUMNS

The stability of 19 organophosphorus (OP) pesticides was performed using precolumns from the Prospekt (automated on-line solid-phase extraction system) filled with C-18. Several different storage conditions were tested, which included storage at 4 degrees C, at -20 degrees C, and a combination of two conditions where precolumns were stored at 4 degrees C for 1.5 months and held at room temperature until analysis (0.5 and 1 month). Complete recovery was observed in precolumns kept in at -20 degrees C for 8 months except for mevinphos, dichlorvos, and phosmet, which had recoveries from 22 to 58%. Degradation also occurred for these same OP pesticides when precolumns were stored at 4 degrees C for 2 months and at room temperature for 1 month, with losses varying from 21 to 78% and from 41 to 61%, respectively. Complete degradation of fenamiphos and fonofos occurred in precolumns stored at 4 degrees C and at room temperature. The stability of the pesticides in each storing treatment is related to the hydrolytic processes, to K-oc, and to their solubility in water.