Analysis of fenthion in postmortem samples by HPLC with diode-array detection and GC-MS using solid-phase extraction

Fenthion (O,O-dimethyl-O-[3-methyl-4-(methylthio)-phenyl-thiophos- phate) is an organophosphate insecticide. A specific method for quantitate fenthion, in postmortem matrices with solid-phase extraction combined with high-performance liquid chromatography-diode-array detection (HPLC-DAD) and gas chromatography-mass spectrometry (GC-MS) is presented. Fenitrothion (O,O- dimethyl-O-[3-methyl-4- nitrophenyl]-thiophosphate) is selected as the internal standard. For sample cleanup, a simple but selective solid-phase exraction is chosen after comparison with traditional liquid-liquid extraction procedures. Homogenized and appropriately diluted aqueous samples are applied, and the analytes are desorbed with 5 mL of dichloromethane. Aliquots of the extract are used for HPLC-DAD and GC-MS analysis. Liquid and GC conditions are as follows: gradient elution with a mixture of methanol and water (10:90 to 90:10, v/v) containing 0.0125M NaOH on an Aluspher RP-Select B column monitoring at 250 nm, and temperature programming from 60 to 300°C on a dimethylpolysi1oxane column in the SCAN mode, respectively. This method is applied to a suicidal case involving unsuspected acute intoxication with fenthion (concentration in blood, 3.8 μg/mL).