Fast Trace Detection of Chlorpyrifos Vapors Using a Handheld Ion Mobility Spectrometer Operated near Ambient Temperature

Chlorpyrifos CPF (O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate), known also as Chlorpyrifos-ethyl, is one of the most utilized organophosphorus pesticides worldwide. Additionally, CPF could be used as a chemical warfare agent surrogate. Although its acute toxicity is not high, it is responsible for both a large number of intoxications and chronic, delayed neurological effects. In this work, it is reported for the first time the qualitative and quantitative response produced by CPF vapors, using a pocket-held Time-of-Flight Ion Mobility Spectrometer (ToF IMS) with a non-radioactive ionization source and ammonia doping, model LCD-3.2E (Smiths Detection Ltd.), operated near ambient temperature (below 30 °C). Spectra of CPF in positive ion mode included two distinct product ion peaks; thus, identification of CPF vapors by IMS relies on these peaks-the monomer M·NH₄⁺ with reduced ion mobility K₀ = ca. 1.76 cm² V^-1 s^-1 and the dimer M₂·NH₄⁺ with K₀ = ca. 1.47 cm² V^-1 s^-1 (where M may be assignable to CPF molecule)-and positive reactant ions (Pos RIP) have K₀ = ca. 2.25 cm² V^-1 s^-1. Excellent sensitivity, with a limit of detection LOD of 0.72 ppb_v (10.5 μg m^-3) and a limit of quantification LOQ of 2.41 ppb_v (35.1 μg m^-3), has been noticed; linear response was up to 100 ppb_v, while saturation occurs over ca. 1000 ppb_v (14.6 mg m^-3). Our results demonstrate that this method provides a robust tool for both off-site and on-site detecting and quantifying CPF vapors at trace levels, which has strong implications for either industrial hygiene or forensic investigations concerning the pesticide Chlorpyrifos, as well as for monitoring of environmental contamination by organophosphorus pesticides.