Gas Phase Structures of Cationized Imidacloprid and Cationized Chlorpyrifos

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Abstract
Neonicotinoids and organophosphates are important analytes due to their use as insecticides and environmental profiles. Cationized imidacloprid and chlorpyrifos as prototypical examples of these were analyzed with drift tube, traveling wave, trapped ion, and cyclic ion mobility mass spectrometry, with experimental collision cross sections (ExpCCSN2) derived for each to help understand their gas phase structures. The ExpCCSN2 of potassiated imidacloprid and potassiated chlorpyrifos are reported for the first time. The cross-platform ExpCCSN2 for [imidacloprid + K]+ is 160–165 Å2 and for [chlorpyrifos + K]+ is 175–176 Å2. Consistent assignment of the [imidacloprid + H]+ structure is achieved based on combining evidence from current work, literature interlaboratory CCS values, DFT energetics, predicted CCS (CalcCCSN2) and literature infrared multiple photon dissociation (IRMPD) spectroscopy. As expected, all cationized species here form charge solvated structures in the gas phase. Imidacloprid coordinates all three cations at the pyridinic N, with a varying degree of nitroguanidine non-covalent interaction for each, depending on the cation. Sodiated and potassiated imidacloprid ions have a 10-membered ring structure where the overall size trend depends more on the non-covalent interaction with nitroguanidine than the incorporated cation size, resulting in different structures. Chlorpyrifos also coordinates cations at the N, but consistently forms 6-membered ring structures. Sodiated and potassiated species change in size relative to the size of the incorporated cation. The consistency of interlaboratory results and current results also support confident assignment for the protomer of [chlorpyrifos + H]+.
Funding Information
  • Australian Research Council (DE170100677)
  • Australian Research Council (FT190100082)
  • University of New South Wales

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