Gas-phase pesticide measurement using iodide ionization time-of-flight mass spectrometry

Abstract

Abstract. Volatilization and subsequent processing in the atmosphere are an important environmental pathway for the transport and chemical fate of pesticides. However, these processes remain a particularly poorly understood component of pesticide lifecycles due to analytical challenges in measuring pesticides in the atmosphere. Most pesticide measurements require long (hours to days) sampling times coupled with offline analysis, inhibiting observation of meteorologically driven events or investigation of rapid oxidation chemistry. Here, we present chemical ionization time-of-flight mass spectrometry with iodide reagent ions as a fast and sensitive measurement of four current-use pesticides. These semivolatile pesticides were calibrated with injections of solutions onto a filter and subsequently volatilized to generate gas-phase analytes. Trifluralin and atrazine are detected as iodide-molecule adducts, while permethrin and metolachlor are detected as adducts between iodide and fragments of the parent analyte molecule. Limits of detection (1 s) are 0.37, 0.67, 0.56, and 1.1 µg m −3 for gas-phase trifluralin, metolachlor, atrazine, and permethrin, respectively. The sensitivities of trifluralin and metolachlor depend on relative humidity, changing as much as 70 and 59, respectively, as relative humidity of the sample air varies from 0 to 80 %. This measurement approach is thus appropriate for laboratory experiments and potentially near-source field measurements.

Constraining the response factors of an extractive electrospray ionization mass spectrometer for near-molecular aerosol speciation

“…Although CIMS is a much "softer" ionization technique than EI, ionization-induced fragmentation still occurs to some extent depending on the analyte, e.g. during protontransfer reaction (PTR) used by the CHARON (Leglise et al, 2019;Murschell et al, 2017;Duncianu et al, 2017). Furthermore, the need for thermal volatilization to convert the particles to vapours before ionization may introduce artefacts from the decomposition of thermally labile compounds (Leglise et al, 2019;Stark et al, 2017;Zhao et al, 2019).…”

Real-Time Measurement of Herbicides in the Atmosphere: A Case Study of MCPA and 2,4-D during Field Application

“…Because the gas-phase basicity of acetic acid is so high, acetate-CIMS is extremely sensitive to organic acids and is well-suited for the phenoxy acid herbicides [28,32,33]. We calibrated the acetate-CIMS in the laboratory with heated solution injections of 2,4-D and MCPA standards (US EPA Pesticide Repository, 99%) diluted in methanol (HPLC grade, Sigma Millipore, Burlington, MA, USA) [21]. 2,4-D is observed as a deprotonated molecular ion (C 8 H 6 Cl 2 O 3 − , m / z 218.96), with a minor contribution from a fragment ion (C 6 H 4 Cl 2 O − , m / z 160.95).…”

“…Off-line analysis of filters or adsorbent cartridges typically involves gas or liquid chromatography coupled to mass spectrometry and can be adequately sensitive for ambient measurements, even in remote locations. However, recent developments in field-portable mass spectrometry enable much faster measurements and offer the potential to directly measure gas-phase pesticides in the atmosphere [21,22].…”

Constraining the response factors of an extractive electrospray ionization mass spectrometer for near-molecular aerosol speciation

“…Although CIMS is a much "softer" ionization technique than EI, ionization-induced fragmentation still occurs to some extent depending on the analyte, e.g. during proton-transfer reactions (PTR) used by a CHARON (Leglise et al, 2019;Murschell et al, 2017;Duncianu et al, 2017). The need for thermal volatilization to convert the particles to vapors before ionization may introduce artefacts from the decomposition of thermally labile compounds (Leglise et al, 2019;Stark et al, 2017).…”