Detection of nitro-based and peroxide-based explosives by fast polarity-switchable ion mobility spectrometer with ion focusing in vicinity of Faraday detector.

Qinghua Zhou,Xin Wang,Dandan Jiang,Liying Peng,Haiyan Wang,Haiyang Li

doi:10.1038/srep10659

Abstract

Ion mobility spectrometer (IMS) has been widely deployed for on-site detection of explosives. The common nitro-based explosives are usually detected by negative IMS while the emerging peroxide-based explosives are better detected by positive IMS. In this study, a fast polarity-switchable IMS was constructed to detect these two explosive species in a single measurement. As the large traditional Faraday detector would cause a trailing reactant ion peak (RIP), a Faraday detector with ion focusing in vicinity was developed by reducing the detector radius to 3.3 mm and increasing the voltage difference between aperture grid and its front guard ring to 591 V, which could remove trailing peaks from RIP without loss of signal intensity. This fast polarity-switchable IMS with ion focusing in vicinity of Faraday detector was employed to detect a mixture of 10 ng 2,4,6-trinitrotoluene (TNT) and 50 ng hexamethylene triperoxide diamine (HMTD) by polarity-switching, and the result suggested that [TNT-H]− and [HMTD+H]+ could be detected in a single measurement. Furthermore, the removal of trailing peaks from RIP by the Faraday detector with ion focusing in vicinity also promised the accurate identification of KClO4, KNO3 and S in common inorganic explosives, whose product ion peaks were fairly adjacent to RIP.

Highlights

The signal amplitude at a highly increased resolution[12]
Ion density, defined as the division of the area of reactant ion peak (RIP) by the area of detector, is maximal at the central detector, and gradually declines for the detector away from the central axis of drift tube, which agrees to the previous works by Eiceman and Davila[19,21]
It is notable that the drift time of RIP shifts to the longer one, and the full width at half maximum (FWHM) of RIP is widened as dx is increased

Summary

Introduction

The signal amplitude at a highly increased resolution[12]. Whereas in our polarity-switching test, due to the effect of accumulated charges, a much longer time was needed for the drift tube with thin metal guard rings to recover its IMS signal after polarity-switching (see supplementary information Fig. S1), which indicates that drift tube with thick metal guard rings might be more suitable for constructing a polarity-switchable IMS. Eiceman and Davila et al experimentally measured the radial ion density profiles in the 63Ni ionization IMS using a charge accumulation IonCCD detector with imaging capability of 2126 pixels at each 21 μ m width, suggesting that the ion density was highest at the center of detector while declined radially[19,21]. This result was in contradiction with the work by Karpas et al.[24] in which the ion density at the center of detector was lower than its outer parts. The detection of KClO4, KNO3 and S in common inorganic explosives, such as black powder was achieved

Methods

Results

Conclusion