application development and performance optimization of ims detector through an alternating ion shutter and rapidly heated drift tube

Abstract: ion mobility spectrometry (ims) is an analytical method used to detect the presence of materials based on the mobility of product ions within an electric field. in this method, first the sample evaporates and then the gas molecules are ionized. the resulting ions are directed to the drift zone through an ion shutter and move towards the detector under the influence of an electric field. qualitative and quantitative analysis and measurement of these molecules is done on the basis of analytical separation resulting from different ionic mobility of different molecules. ims is one of the paramount methods for detecting and identifying traces of explosives, narcotics, and chemical warfare agents. this device is made in both stationary and portable forms, which has been highly utilized in the fields of military, security and environmental measurements [1]. institute of materials and energy, iranian space research center has several decades of experience in the field of designing and manufacturing detector devices based on ims technology, which has successfully developed it in various fields including device miniaturization, software upgrade, device performance optimization, and the ability to quickly switch between positive and negative modes, as well as the design and manufacture of portable instruments. the detection of some important and widely used substances by ims technology has been faced with challenges. one of these substances is ammonium nitrate which due to the production of a peak very close to the air peak, practically overlaps with air peak and it is not possible to separate and detect it by ims. the proposed methods to detect ammonium nitrate generally include the use of some other technologies in addition to ims and the implementation of some hardware changes, which generally add to the complexity of the device [2-3]. in the present study an attempt was made to detect ammonium nitrate without applying these complex changes and only by using a software method. indeed, through alternating ion shutter pulses we could control the concentration of ammonium nitrate introduced to the drift tube and detect this strategic explosive without scarifying sensitivity. the accuracy of the method was confirmed in field applications of the device. in addition, ims drift tubes generally work at high temperature, which will cause a relatively long initial warm-up time (about 30 minutes in typical commercial devices). in order to obviate this problem, a drift tube was designed and constructed through which the warm-up time of the device was reduced to less than 15 minutes, and practically a big step was taken in the direction of better operational use of this device.