Novel ion drift tube for high-performance ion mobility spectrometers based on a composite material
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ORIGINAL RESEARCH
Novel ion drift tube for high-performance ion mobility spectrometers based on a composite material André Ahrens 1
&
Janina Möhle 1 & Moritz Hitzemann 1
&
Stefan Zimmermann 1
Received: 26 May 2020 / Revised: 24 June 2020 / Accepted: 26 June 2020 # The Author(s) 2020
Abstract Ion mobility spectrometers (IMS) are able to detect pptV-level concentrations of substances in gasses and in liquids within seconds. Due to the continuous increase in analytical performance and reduction of the instrument size, IMS are established nowadays in a variety of analytical field applications. In order to reduce the manufacturing effort and further enhance their widespread use, we have developed a simple manufacturing process for drift tubes based on a composite material. This composite material consists of alternating layers of metal sheets and insulator material, which are connected to each other in a mechanically stable and gastight manner. Furthermore, this approach allows the production of ion drift tubes in just a few steps from a single piece of material, thus reducing the manufacturing costs and efforts. Here, a drift tube ion mobility spectrometer based on such a composite material is presented. Although its outer dimensions are just 15 mm × 15 mm in cross section and 57 mm in length, it has high resolving power of Rp = 62 and detection limits in the pptV-range, demonstrated for ethanol and 1,2,3-trichloropropane. Keywords Miniaturized . Ion mobility spectrometer . Drift tube . Composite material . High-performance . Low-cost
Introduction Ion mobility spectrometers (IMS) are compact analytical instruments, mainly for the rapid detection of volatile and semivolatile substances at trace levels in the range of pptV (partsper-trillion by volume) within a few seconds [1, 2]. Equipped with electrospray ionization, IMS are also used for measuring larger molecules in liquids [3–5]. Drift tube IMS separate ions in the gas phase under the influence of a homogeneous electric field. A basic setup of a drift tube IMS is shown in Fig. 1. For analysis, the sample is ionized by an ionization source. The ionized sample is then injected into the drift region. Subsequently, driven by the electric field, ions move along the axis of a drift tube through a neutral drift gas and are separated according to their ion mobility. At the end of the ion drift tube, the ions discharge at a detector, often a Faraday plate, and the resulting ion current is recorded over time giving an ion mobility spectrum. At low electric fields, the ion * André Ahrens [email protected] 1
Institute of Electrical Engineering and Measurement Technology, Department of Sensors and Measurement Technology, Leibniz University Hannover, Appelstr. 9A, 30167 Hannover, Germany
mobility K is a constant. It is defined as the proportionality factor between the drift velocity vd of the ions and the electric field strength E [6]. As shown in Eq. (1), the ion mobility can thus be derived from the length L of drift tube, the drift voltage Ud and the drift
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