Characterisation of the ion mobility spectrometric behaviour of a dinitrobutane under varying conditions of temperature and concentration

The decomposition of 2,3-dimethyl-2,3-dinitrobutane in an ion mobility spectrometer operating in the positive and negative modes is described. The results of: varying the concentration of 2,3-dimethyl-2,3-dinitrobutane between 0 and 0.12 mg m(-3) in nitrogen; varying the temperature between 317 and 455 K; and the effects of water, dichloromethane and ammonia reactant ion chemistries on the response of an ion mobility spectrometer are reported. The observed behaviour is consistent with the decomposition of 2,3-dimethyl-2,3-dinitrobutane to 3-methyl-3-nitrobut-1-ene and then to 2,3-dimethylbut-1,3-diene in a two stage process. Molecular ions with reduced mobilities attributable to species based on NO2- are also observed simultaneously in the negative mode, supporting the proposed decomposition mechanism. The activation energies for the decomposition process, estimated from temperature programmed ion mobility spectrometry, are found to be lower than that previously reported. This may be attributed to the electron withdrawing nature of the hydrated proton in the molecular cluster ion. (C) 1998 Elsevier Science B.V. All rights reserved.