Analysis of explosives using corona discharge ionization combined with ion mobility spectrometry–mass spectrometry Jihyeon Lee a , Sehwan Park a , Soo Gyeong Cho b , Eun Mee Goh b , Sungman Lee c , Sung-Suk Koh c , Jeongkwon Kim a,n a Department of Chemistry, Chungnam National University, Daejeon, Republic of Korea b Agency for Defense Development, Daejeon 305-600, Republic of Korea c Sensor Tech Inc., Kyunggi-Do 462-713, Republic of Korea article info Article history: Received 16 October 2013 Received in revised form 20 November 2013 Accepted 21 November 2013 Available online 28 November 2013 Keywords: Explosives Corona discharge ionization Ion mobility spectrometry Mass spectrometry abstract Corona discharge ionization combined with ion mobility spectrometry–mass spectrometry (IMS–MS) was utilized to investigate five common explosives: cyclonite (RDX), trinitrotoluene (TNT), pentaery- thritol tetranitrate (PETN), cyclotetramethylenetetranitramine (HMX), and 2,4-dinitrotoluene (DNT). The MS scan and the selected ion IMS analyses confirmed the identities of the existing ion species and their drift times. The ions observed were RDX Á NO 3 À , TNT À , PETN Á NO 3 À , HMX Á NO 3 À , and DNT À , with average drift times of 6.93 ms, 10.20 ms, 9.15 ms, 12.24ms, 11.30 ms, and 8.89 ms, respectively. The reduced ion mobility values, determined from a standard curve calculated by linear regression of (normalized drift times) À1 versus literature K 0 values, were 2.09, 1.38, 1.55, 1.15, 1.25, and 1.60 cm 2 V À1 s À1 , respectively. The detection limits were found to be 0.1 ng for RDX, 10 ng for TNT, 0.5 ng for PETN, 5.0 ng for HMX, and 10 ng for DNT. Simplified chromatograms were observed when nitrogen, as opposed to air, was used as the drift gas, but the detection limits were approximately 10 times worse (i.e., less sensitivity of detection). & 2013 Elsevier B.V. All rights reserved. 1. Introduction Ion mobility spectrometry (IMS) is frequently used for the detection of explosives, illegal drugs, and chemical warfare agents [1,2] because it uses equipment that is small and simple to operate. The most common ionization source for the analysis of explosives by IMS is radioactive 63 Ni, used to ionize explosive vapors [1]. However, the health risks of 63 Ni, as well as low ion signals, have led many researchers to investigate other ionization techniques for analyzing explosives. Two alternatives to 63 Ni as an ionization source are corona discharge and secondary electrospray ionization (for a review, see [3]). Corona discharge provides an approximately 100-fold greater electron current than 63 Ni [4]. Recently, corona discharge ionization was coupled with IMS to analyze explosives [4–6]. Mass spectrometry (MS) is popularly used to analyze explosives because of its accuracy in identifying explosives from the m/z values [7]. Several groups have attempted to combine IMS with MS (IMS–MS) for the analysis of explosives [3,8–10]. IMS–MS is a powerful technique because it determines ion mobility and m/z values simultaneously. In the current study, corona discharge ionization combined with IMS–MS was used to examine five explosives: cyclonite (RDX), trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), cyclotetramethylenetetranitramine (HMX), and 2,4-dinitrotoluene (DNT). 2. Experimental 2.1. Materials and chemicals RDX, TNT, PETN, HMX, and DNT, shown in Fig. 1, were obtained from the Agency for Defense Development (Daejeon, Korea). Acetonitrile (ACN), used as the solvent, was purchased from Sigma-Aldrich (St. Louis, MO, USA). 2.2. Instrument IMS–MS was performed using an RA4100 ion mobility spectro- meter (Excellims, Acton, MA, USA) equipped with quadrupole MS and corona discharge ionization in negative ion mode. The operating conditions were as follows: source voltage, À 10.9 kV; drift tube voltage, À 8.9 kV; gate width, 70 μs; and temperature of the desorber and drift tube, 180 1C. The drift length, or the distance from the gate to the detector, was 10.5 cm. Details of the drift tube have been published by Excellims [11]. Purified dry air was used as the drift gas in most of the experiments, although some experiments used nitrogen gas for comparison. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta 0039-9140/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.talanta.2013.11.059 n Correspondence to: Department of Chemistry, Chungnam National University, 99 Daehak-Ro, Yuseong-Gu, Daejeon 305-764, Republic of Korea. Tel.: 82 42 821 5477; fax: 82 42 821 8896. E-mail address: jkkim48105@cnu.ac.kr (J. Kim). Talanta 120 (2014) 64–70