The assignment of the peaks in the ion mobility spectrum of a compound without using mass spectrometry techniques is very difficult and in some cases is impossible. Ions are at atmospheric pressure in the ionization region of ion mobility spectrometer (IMS). Different processes such as hydration of ions, fragmentation of molecule due to the protonation and temperature and clustering reactions occurs in IMS and cause difficulties in assignment of ion mobility spectra. In this work, a semi-empirical method was introduced for the analysis of the ion mobility spectra. In this method, an ion which its peak is known in the spectrum is selected as the reference ion. The reactant ion [NH 4 (H 2 O) n ] + was selected as the reference ion to estimate the drift time of the other ions. The average orientationally cross sectio of the ion and the reactant ion along with the experimental drift time of the reactant ion is necessary. The other advantage of this method is the estimation of the degrees of hydration of the ions in the cell of IMS and its variation with the temperature. In this work the ion mobility spectra of methyl isobutyl ketone (MIBK), cycloheptanone and vitamin B6 were analyzed.
