Gas-Phase Pesticide Measurement Using Iodide Ionization Time-of-Flight Mass Spectrometry
Pesticides are important analytical targets for environmental regulators, researchers, and agricultural scientists, and because of their acutely harmful health effects, often need to be measured at trace levels. However, they are analytically challenging to measure, and conventional measurement techniques are slow and laborious. Researchers at Colorado State University have developed a method to measure pesticides sensitively, quickly, and directly (with no sample preparation), based on iodide chemical ionization time-of-flight mass spectrometry (I- CI-TOFMS). With a one-second measurement interval, they were able to demonstrate limits of detection (LOD) for the pesticides and herbicides trifluralin, metolachlor, atrazine, and permethrin at 0.37, 0.67, 0.56, and 1.1 μg m-3, respectively (equivalent to 120, 50, 110, and 150 ppt).
The authors chose iodide CI-TOFMS because of its fast time resolution, portability, and high mass resolution, which is necessary to identify the chemical composition of molecules in the 200-500 amu range. Additionally, I- CI-TOFMS had been shown to sensitively detect oxidized nitrogen and halogenated species, semi-volatile organic compounds, and organic acids, which suggested it may be an ideal technique to target pesticides.
To calibrate the instrument, the authors developed a heated liquid-to-vapor sampler using a Teflon filter. One- to six-uL quantities of pesticide solutions were injected into the instrument. TOFWERK’s “Tofware” data analysis package was used to search for and identify ions associated with pesticides. Compounds were identified based on exact mass-to-charge ratio and isotope patterns, and the authors highlight that the isotope analysis enabled by Tofware is key to the measurement of trace concentrations of these substances. The authors conclude that the technique is suitable for measuring pesticides in ambient fine particles and in the gas phase.