Signal decay curves obtained with a pulsed electron gun allow for improved analyte identification power of ion mobility spectrometers by distinction of monomer and dimer signals

Ion mobility spectrometry (IMS) is a well-known technique applied to detect hazardous substances in ambient air. Consequently, it has been used for many years for the detection of chemical warfare agents, toxic substances or illegal drugs. The main advantages are the small size of IMS instruments and the very high sensitivity in the range of a few parts per billion. However, one major disadvantage is the fairly difficult interpretation of spectra especially when mixtures of substances are involved. Spectra recorded with a pulsed IMS, in which delay times can be inserted between ion formation and ion detection, can simplify this task due to the distinct behavior that monomer and dimer peaks exhibit with varying delay times. The discrimination between monomer and dimer signals would normally require further experimental efforts (e.g. a mass spectrometer) with disadvantages regarding the portability of the device. This paper describes how a pulsed electron gun used in a standard IMS device allows for this discrimination without compromising any of the benefits IMS devices offer.