Dual-drift Tube Ion Mobility Spectrometry Based on Corona Discharge Ionization Source

Abstract

Ion mobility spectrometry (IMS) is a trace detection technique operating at atmospheric pressure. It is widely utilized in various fields, such as explosives and drug detection, chemical warfare agent detection, and biomedical applications, due to its fast response time and high sensitivity. The various of substances can be identified through analyzing the discrepancies in the drift time of charged particles in an electric field. Depending on the polarity of the charged particles, it can operate under either positive or negative ion mode. Currently, the majority of IMS operate in only one detection mode. For example, explosives detection operates under negative ion mode, while drug detection operates under positive ion mode. However, single detection mode system is prone to miss detections because some substances may differentially respond to positive and negative detection modes. Simultaneous detection under both positive and negative ion modes can further enhance detection accuracy. In this study, a dual-drift tube ion mobility spectrometry capable of simultaneously detecting positive and negative ions was constructed using corona discharge ionization source technology and a compact dual ion-gated pulse control circuit. The instrument parameters of IMS were optimized, while simultaneously determined hexogen, methamphetamine and the metabolite of trinitrotoluene (TNT)，2,4-diamino-6-nitrotoluene (2,4-DANT). The optimal experimental conditions were selected as follows: a drift gas flow rate of 600 mL/min, a carrier gas flow rate of 500 mL/min, a drift tube temperature of 100 ℃, and a thermal desorption temperature of 200 ℃. The reduced mobility values of 1.72 cm2/V·s and 1.44 cm2/V·s are obtained through the detection of explosive hexogen (RDX) and drug methamphetamine (MA), respectively. These values agree well with the reported values, thereby proving the reliability of the instrument’s detection. Finally, the performance of the developed instrument was evaluated using 2,4-DANT, this substance that can be detected under both positive and negative ion modes. Production peaks are observed in both modes, and the normalized mobility values for 2,4-DANT are reported as approximately 1.67 cm2/V·s and 1.33 cm2/V·s under positive and negative ion modes, respectively. Through exploring the detection limits for both positive and negative ions, it was revealed that the homemade dual ion mobility spectrometer is capable of simultaneous detection of both positive and negative ions, achieves the lowest detection limits of 200 pg and 260 pg for 2,4-DANT, respectively. Importantly, these detection limits are not significantly compromised by sample division, which underscores the broad applicability and value of the instrument, highlighting its potential in various fields.

Keywords

• ion mobility spectrometry (ims)
• corona discharge
• ion gate
• dual drift tube
• simultaneous detection of positive and negative