The sublimation/vaporization of the protic ionic liquid 1,1,3,3-tetramethylguanidinium chloride, [Htmg]Cl, was studied by Fourier transform ion cyclotron. resonance mass spectrometry in the temperature range 298-488 K and under a reduced pressure of 3.2 x 10(-6) to 1.5 x 10(-5) Pa. The results show that no charged species are present in the vapor over the condensed phase. Furthermore, ion-molecule reaction studies found no evidence of neutral ion pairs in the gas phase. This indicates that the sublimation/vaporization of [Htmg]Cl conforms to the general mechanism postulated for the distillation of protic ionic liquids, which involves a proton transfer leading to the formation of the neutral acid and base precursors, in this case hydrogen chloride and 1,1,3,3-tetramethylguanidine.