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 five synthetic pyrethroid insecticides in soil is developed and method performance data presented. The pyrethroid residues were extracted with hexane-dichloromethane in an ultrasonic bath. The extract was cleaned up on a Florisil column prior to determination by gas chromatography-negative-ion chemical ionization mass spectrometry (GC-NICI-MS) in selected-ion monitoring (SIM) mode. The highest detection sensitivities were achieved in the SIM mode where the instrument was adjusted to collect only a few ions which were indicative for the compound to be searched for, instead of scanning the entire spectrum over the whole mass range. The gain in sensitivity was the result of longer specific sampling times for each of the ions selected. Recovery studies were performed at 10, 50 and 100 ppb fortification levels of each pyrethroid and of the internal standard, mirex, and the percentage recoveries ranged from 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 collected from the environment of a River Catchment being currently monitored for the presence of target pyrethroids.