Analysis of fire ant pesticides in water by solid-phase microextraction and gas chromatography/mass spectrometry or high-performance liquid chromatography/mass spectrometry

The analysis of four widely used fire ant pesticides (chlorpyrifos, fenoxycarb, avermectin, and hydramethylnon) in water was accomplished by combining solid-phase microextraction (SPME) with either gas chromatography/quadruple ion trap mass spectrometry (GC/MS) or high-performance liquid chromatography/quadruple ion trap MS (HPLC/MS). Solid-phase microextraction is a fast, selective, and solvent-free extraction technique that accomplishes both extraction and pre-concentration events in a single step. These features allowed the methods developed to be sensitive, with calculated LOD of 10ng/l for chlorpyrifos, 80ng/l for fenoxycarb, 100ng/l for avermectin, and 1µg/l for hydramethylnon, each obtained from only 10min extractions from standards in water. These values represent an improvement of an order of magnitude in detection limits for avermectin and hydramethylnon compared to those reported previously. The methods were shown to be linear in the range of 100ng/l-100µg/l for chlorpyrifos and fenoxycarb, 1µg/l-1mg/l for avermectin, and 10µg/l-1mg/l for hydramethylnon. These methods were applied to the analysis of water samples to which commercial fire ant bait preparations had been added and to runoff water collected from a lawn. Quantitative analyses were performed for chlorpyrifos, fenoxycarb, and avermectin, as the pesticides in the water samples were monitored for ~9 days to almost 2 months. However, due to poor precision of the method for hydramethylnon, only qualitative data were obtained.