Ion mobility spectrometers with doped gases

Ion mobility spectrometry (IMS) is an instrumental technique used successfully for the detection of wide range of organic compounds in the gas phase. In this paper, advances in using special substances called dopants for gases flowing through IMS detectors are reviewed. These substances influence the ion-molecule chemistry in sample ionisation region as well as change conditions for the drift of ions. Improved selectivity and sensitivity of detection can be obtained by the use of dopants. In some cases, especially when measurements are conducted in the presence of different substances disturbing detection, the use of dopants is indispensable. The theory of the function of dopants is based on the knowledge of ion-molecule reactions. Fundamental information about these reactions is presented here. Mechanisms of changing the composition of ions produced in reactant section of IMS detector are explained on this basis. The most commonly used dopants are acetone and ammonia for positive mode and chloride for negative mode IMS. Other substances, such as higher ketones, organophosphorous compounds or methyl salicylate are used for special purposes and are selected for given analytical problem. Particular examples for the application of these substances are described.