design and construction of a pulsed corona ionization source for ims detector

Abstract: ion mobility spectrometry (ims) is a technique for qualitative and semi-quantitative measurement of organic chemical compounds. this system includes ionizing the molecules and materials resulting from decomposition and drifting these particles in an electric field. qualitative and quantitative analysis and measurement of these molecules are based on the different ionic mobility of various molecules. stationary and portable ims applications in military, security, and environmental measurements have attracted the attention of many researchers to study and work in this field [1]. for a long time, radioactive radiation (such as 63ni) was used as a source of ionization in these systems. due to the specific issues of these sources, many researchers have been looking for suitable non-radioactive alternatives to be used as an ionization source in ims. as a suitable replacement for the old radioactive systems, the phenomenon of corona discharge was considered. the research on ims ionization sources in the air has revealed that the reactants in the positive corona discharge mode are the same as those in the old radioactive ionization source. recently, the use of pulsed corona discharge as a source of ionization was considered. in this method, electric pulses are used to create corona discharge. these pulses are created by applying a voltage jump (from several hundreds of volts to several kilovolts) in pulse form on two electrodes that are biased with an initial dc voltage (from zero to several kilovolts). the energy needed in pulse corona discharge will be used for the production of electron-ion pairs and not to drive the ions towards the cathode electrode. minimizing this effect which is dominant in continuous corona, will greatly improve the energy for producing ions. another advantage of pulse corona source is the possibility of removing the injection grid in the ims cell [2]. there are two major advantages of using gridless ims cells: firstly, the number of ions entering the drift region is greatly increased. this increase is due to the elimination of ion losses on the grids, which will cause more effective use of produced ions and increase the signal-to-noise ratio in ims. secondly, removing the electronic, mechanical, and software parts related to the injection grid will reduce the peripheral equipment used in ims. the two mentioned factors will play a very important role in miniaturization and optimization of ims systems [3]. accordingly, this study is dedicated to the structural development and replacement of the ims ionization source.