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 ( Exp CCS N2 ) derived for each to help understand their gas phase structures. The Exp CCS N2 of potassiated imidacloprid and chlorpyrifos are reported for the first time. The cross-platform Exp CCS N2 for [imidacloprid+K] + is 160−165 Ų and for [chlorpyrifos+K] + is 175–176 Ų. Consistent assignment of [imidacloprid+H] + structure is achieved based on current work, literature interlaboratory CCS values, DFT energetics, predicted CCS ( Calc CCS N2 ) and literature IRMPD spectroscopy. Imidacloprid coordinates cations at the pyridinic N, with a varying degree of nitroguanidine interaction that depends on the cation. Sodiated and potassiated imidacloprid ions have a 10-membered ring structure where the overall size depends more on the non-covalent interactions than the incorporated cation size. Chlorpyrifos also coordinates cations at the N, but consistently forms 6-membered ring structures. Overall size trends for sodiated and potassiated species follow the cation size trends, revealing the change in size due to incorporated cation. The consistency of interlaboratory results and current results also support confident assignment for the protomer of [chlorpyrifos+H] + .