HPLC methods for quantifying depositions from aerosol pesticide applications

Abstract: Aerosol treatments of food processing facilities is one method of pest management
with some aerosols containing the insect growth regulator, methoprene. Research studies were conducted about on aerosol distribution using electronic instrumentation deployed to measure portions of the sprays near the floor and at various locations in a test facility. Instruments require calibration to relate measurements to actual depositions and HPLC (high performance liquid chromatography) was conceived as a method to do this. To test this aerosol spray deposits were collected from large petri dishes on the floor that were layered with flour, ~ 3.5g, and adjacent to an electronic aerosol measuring instrument. After the aerosol had settled, the dishes were collected and taken for HPLC analysis of the methoprene contained in the flour. Flour from each petri dish was emptied into a 50 ml centrifuge tube along with 40 ml of methanol and mixed, then followed by centrifuging. A historic method was found from literature for testing methoprene on tobacco leave and used 120 min mixing time and 48 hours holding time for preparation of batch of samples. Several experiments were performed to test mixing and holding times. We found that sample processing time could be reduced to 30 min mixing time and 0 holding time and still obtain greater than 90 % recovery of the methoprene. Spray trials were performed which provided a range of depositions. For the aerosol pesticide studied, typical depositions after treatments were ~ 7-8 ppm methoprene per dish. The HPLC method could detect methoprene concentrations down to 0.2 ppm. It was concluded this HPLC method will provide a good method for comparing and calibrating the methoprene depositions to the electronic aerosol instruments. Furthermore, petri dish deposition sampling could be used by applicators for potentially evaluating methoprene pesticide applications and distributions at food processing facilities.