DETERMINATION AND STABILITY OF PHENMEDIPHAN, ETHOFUMESATE AND FENAMIPHOS IN-GROUND WATER SAMPLES USING AUTOMATED SOLID-PHASE EXTRACTION CARTRIDGES FOLLOWED BY LIQUID-CHROMATOGRAPHY HIGH-FLOW PNEUMATICALLY ASSISTED ELECTROSPRAY MASS-SPECTROMETRY

The determination and stability of polar pesticides phenmediphan, etho fumesate and fenamiphos in ground water samples was subjected to analy sis with solid phase extraction (SPE) followed by liquid chromatograph y-high flow pneumatically assisted electrospray mass spectrometry (LC- ESP-MS). Pesticides were spiked at 6 mu g/L in ground water samples an d 80 mt were preconcentrated by using an Automated Sample Preparation with Extraction Columns (ASPEC XL) system. After preconcentration, sev eral different storage conditions were tested, which included storage at 4 degrees C, at -20 degrees C and at room temperature using styrene divinylbenzene (SDB) cartridges. The percentage of degradation varied from 20 to 80% for all the studied pesticides after 20 days of storag e at room temperature. Phenmediphan and ethofumesate were stable at 4 degrees C and -20 degrees C during all the studied period whereas fena miphos was recovered only 32 and 50% at 4 degrees C and -20 degrees C, respectively, after 80 days of storage. The L.O.D under LC-ESP-MS and SIM conditions were between 10-20 pg, 5-60 times lower as compared to LC-thermospray-MS with no thermal degradation of phenmediphan. This h igher sensitivity of LC-ESP-MS permitted the determination of fenamiph os sulphoxide formed during the extraction and storage and the identif ication of the interferences present in the cartridges e. g., diethyl and di-n-butyl phthalates.