Study on temperature-responsive characteristics of reactant ions in corona discharge ion mobility spectrometry

Ion mobility spectrometry (IMS) is an analytical technique and can separate gas-phase ions under atmospheric pressure conditions. Using a laboratory-built direct-current positive corona discharge ion mobility spectrometer (CD-IMS), this study investigates the relationship between reactant ions and temperature when environmental air is used as the buffer gas. Quantum chemical calculations are employed to interpret the experimental observations, such as the initial intensities of ion peaks and their variations with temperature, thereby elucidating the mechanisms by which reactant ions respond to temperature changes. Experimental results indicate that the hydrated cluster ions NH₄⁺(H₂O)_n, NO⁺(H₂O)_n, H₃O⁺(H₂O)_n and O₂⁺(H₂O)_n exhibit distinct responses to temperature variations due to processes such as thermal dissociation and transformation into hydronium ions upon reaching certain hydration numbers. Specifically, NH₄⁺(H₂O)_n and NO⁺(H₂O)_n disappear when the temperature rises to 383 K, while O₂⁺(H₂O)_n disappears at 413 K. In contrast, H₃O⁺(H₂O)_n persists throughout the temperature range and displays a trend of an initial decrease followed by a continuous increase in intensity. Additionally, the drift times of NH₄⁺(H₂O)_n, H₃O⁺(H₂O)_n and O₂⁺(H₂O)_n generally decrease with rising temperature, whereas that of NO⁺(H₂O)_n slightly increases.