Pyrethroid soil extraction, properties of mixed solvents and time profiles using GC/MS-NICI analysis

Ultrasonic extraction was used to develop a suitable binary solvent system for the analysis of synthetic pyrethroid pesticides and mirex on soil. The analysis was carried out by gas chromatography with negative ion chemical ionization mass spectrometry (GC/MS-NICI). In the initial experiments, accurately weighed soil samples were spiked with a mixture of standard solution pyrethroids and mirex and shaken for 24 h to ensure homogeneity, then extracted with solvent. The extracts were evaporated to dryness before the volumetric internal standard was added. The binary solvents used in this study were various mixtures of hexane : acetone, hexane : dichloromethane (DCM), isooctane : acetone and isooctane : dichloromethane, representing different classes of polarity. The recoveries of all pyrethroids and mirex were satisfactory over three solvent systems: hexane : acetone, hexane : DCM and isooctane : acetone, but results of isooctane : DCM produced low recoveries. The average recovery increased with the extraction time, but the increase was not statistically significant. A 30-min optimum extraction was deemed sufficient for recovering pyrethroids from soil. After 30 min, extraction decreased owing to the re-distribution of the analyte on the soil matrix.