ANALYTICAL METHOD DEVELOPMENT FOR THE DETERMINATION OF SYNTHETIC PYRETHROID INSECTICIDES IN SOIL BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY OPERATED IN NEGATIVE-ION CHEMICAL-IONIZATION MODE

An effective analytical method for the simultaneous determination of f ive synthetic pyrethroid insecticides in soil is developed and method performance data presented. The pyrethroid residues were extracted wit h hexane-dichloromethane in an ultrasonic bath. The extract was cleane d up on a Florisil column prior to determination by gas chromatography -negative-ion chemical ionization mass spectrometry (GC-NICI-MS) in se lected-ion monitoring (SIM) mode. The highest detection sensitivities were achieved in the SIM mode where the instrument was adjusted to col lect only a few ions which were indicative for the compound to be sear ched for, instead of scanning the entire spectrum over the whole mass range. The gain in sensitivity was the result of longer specific sampl ing times for each of the ions selected. Recovery studies were perform ed at 10, 50 and 100 ppb fortification levels of each pyrethroid and o f the internal standard, mirex, and the percentage recoveries ranged f rom 81.7+/-4.2 to 108.2+/-2.6%. Four determinations were made at each concentration level along with a procedural blank. The quantification limit of the method was in the range of 0.012 to 4.4 ppb, depending on the compound. This method was also applied to sediment samples collec ted from the environment of a River Catchment being currently monitore d for the presence of target pyrethroids.