Cationized Imidacloprid and Chlorpyrifos via Cross-Platform Ion Mobility-Mass Spectrometry

The gas-phase cross-platform collision cross sections (CCS) of cationized (protonated, sodiated, and potassiated) imidacloprid and chlorpyrifos were analyzed with single- and multi-field drift tube, traveling wave, trapped ion, and cyclic ion mobility mass spectrometry. The experimental cross-platform CCS are in the range of: [imidacloprid+H]+ = 154−158 Å; [imidacloprid+Na]+ = 158–160 Ų; [imidacloprid+K]+ = 160−165 Ų; [chlorpyrifos+H]+ = 163−166 Ų; [chlorpyrifos+Na]+ = 170−173 Ų, and [chlorpyrifos+K]+ = 175–176 Ų, and are within ~3% of each other and inter-laboratory values. DFT predicts imidacloprid coordinates cations at the pyridinic N, with a degree of nitroguanidine interaction that depends on the cation, while chlorpyrifos also coordinates cations at the N, but consistently forms 6-membered ring structures. The theoretically predicted CCS of protonated imidacloprid deviated significantly (7−10%) from the experimental CCS. In contrast, sodiated and potassiated imidacloprid ions’ theoretically predicted CCS were consistent (2−3%) with the experimental CCS, supporting a more compact 9-membered ring-shaped structure compared to the protonated congener. On the other hand, predicted CCS for protonated chlorpyrifos matched the experimental CCS well (2−5%), but sodiated and potassiated chlorpyrifos had less agreement between calculated and experimental CCS (>5.5%), however structural trends are reproduced. While cross-platform variations are minimal, discrepancies in predicted CCS highlight the need for standardized protocols before CCS can reliably identify pesticide residues.