Sprayed liquid–gas extraction of semi-volatile organophosphate malathion from air and contaminated surfaces

Abstract

In this study, a new air sampling method termed sprayed liquid–gas extraction (SLGE) was developed for semi-volatile organic compounds. Water droplets with an average diameter of less than 10 μm were created, using a flow blurring nebulizer from distilled water and the gas-phase sample. This allowed the fast, simple and highly-efficient enrichment of trace levels of the widely used organophosphate insecticide malathion, which is also an accepted simulant for the potent nerve-agent VX. After spraying, extraction and solvent evaporation, the collected malathion molecules were dissolved in 100 μL organic solvent and analyzed using gas chromatography-mass spectrometry. Different parameters including SLGE duration, gas and extracting-agent flow-rate, humidity and memory effect were evaluated and optimized. The method was compared with standard air-sampling tubes containing XAD-2 and XAD-4 polymers and also the liquid-trapping method. Combining simplicity with cost-effectiveness, the SLGE method shows outstanding extraction efficiency compared to the standard methods. Using the optimized method, the limits of detection (LOD) and quantification (LOQ) were determined to be 7.53 and 25.11 ng L⁻¹, respectively. The developed method was compared to a standard extraction with XAD-2 tube which was run in parallel to the SLGE. These methods were used to extract a mixture of malathion, 2,4-dinitrotoluene (explosive marker), 4-chloro-3-methylphenol, carbaryl (insecticide), dimethoate (organophosphate insecticide), atrazine (herbicide) and permethrin (insecticide) in synthetic air. These compounds were also deposited on a steel plate and a composite building material and the air above these materials was sampled.