The ionization mechanism in dopant-assisted atmospheric pressure photoionization and the effect of solvent on the ionization efficiency was studied using 7 naphthalenes and 13 different solvent systems. The ionization efficiency was 1-2 orders of magnitude higher with dopant than without, indicating that the photoionization of the dopant initiates the ionization process. In positive ion mode, the analytes were ionized either by charge exchange or by proton transfer. Charge exchange was favored for low proton affinity solvents (water, hexane, chloroform), whereas the addition of methanol or acetonitrile to the solvent initiated proton transfer. In negative ion mode, the compounds with high electron affinity were ionized by electron capture or by charge exchange and the compounds with high gas-phase acidity were ionized by proton transfer. In addition, some oxidation reactions were observed. All the reactions leading to ionization of analytes in negative ion mode are initiated by thermal electrons formed in photoionization of toluene. The testing of different solvents showed that addition of buffers such as ammonium acetate, ammonium hydroxide, or acetic acid may suppress ionization in APPI. The reactions are discussed in detail in light of thermodynamic data.

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The species involved in the distillation of aprotic ionic liquids are discussed in light of recent simulations and mass spectrometric data obtained by various techniques. New mass spectrometric data collected via laser-induced acoustic desorption and the thermal desorption of ionic liquids are also presented as well as additional DFT calculations. The available evidence of theoretical simulations and mass spectrometric data suggests that the distillation of ionic liquids occurs mainly via neutral ion pairs of composition CnAn [C(+) = cation and A(-) = anion], followed by gas-phase dissociation to lower order ion pairs and then dissociation of hot CA to C(+) and A(-), followed by ion/molecule association events to give [CnAn-1](+) or [Cn-1An](-) ions to a degree that depends on the amount of internal energy deposited into the neutral CnAn clusters upon evaporation.