Dopants and gas modifiers in ion mobility spectrometry

The ion mobility techniques, including the most commonly used drift-tube ion mobility spectrometry (IMS) and differential mobility spectrometry (DMS), are used successfully for the detection of a wide range of organic compounds in the gas phase. In order to improve detection quality, admixtures are added to gas streams flowing through the detector. Dopants mostly prevent the ionization of interfering chemicals however, better detection may be also achieved by shifting the peaks in the drift-time spectra, enabling ionization of analytes with low proton affinities and, thus, facilitating photoionization. Fundamental information about ion-molecule reactions including the role of dopants is presented. The term 'gas modifiers' refers to substances that influence the ion transport by changing the mobility of ions without changing the chemistry of the ionization. The mechanism of the gas modifier's interaction with an analyte in ion separation in drift tube IMS and DMS is explained in this paper.