Ion mobility spectrometry (IMS) has been an important tool for decades in the field of trace gas analysis of substances such as explosives, drugs of abuse or chemical warfare agents. In recent years, its application has been extended to more complex set ups. In this paper we present the application of a standard IMS device equipped with a novel pulsed electron gun for ionization in the investigation of the chemical warfare agent simulant dimethyl methylphosphonate (DMMP). The signal decay times of the reactant ion peak (RIP), the DMMP monomer and dimer have been investigated. Thus, further information could be obtained of the innovative application of different signal decay times in order to filter out signals of contaminants with focus on the decay dependence on the concentration. Additionally, further details regarding the still not fully understood underlying decay mechanisms have been found.