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Drift tube ion mobility spectrometer

  1. Sep 28, 2014 #1
    Hello PF,

    thanks for having me here. I am working in chemistry and we are building a atmospheric pressure drift tube ion mobility spectrometer.
    The drift tube consists of 20 stacked stainless steel electrodes insulated by PTFE spacers connected via a resistor chain (voltage divider) to produce a (homogeneous) electric field gradient. The tube is approximately 20 cm long. The voltage applied is 5 kV (the current max is 2 mA). The Ion source produces positive ions in the range of a few nA. The pulsed ion detection (via an ion gate) takes place with a faraday plate detector (connected to a transimpedance amplifier/electrometer) at the end of the tube (ground potential). The principle is like in time of flight mass spectrometry but at ambient pressure and the ions collide against a inert drift/washing gas.
    I have questions concerning the electric field (homogeneity), apertures, capacitively decoupling of the ion current in front of the detector and so on. :)
    But I want to start with a question concerning the Resistors in the voltage divider and the resulting current that flows through the resistors when a voltage is applied.
    In the literature the working groups use very high-impedance drift tubes. Here, electrodes are connected via 1 or 5MOhm resistors.
    Does an lower overall impedance of a drift tube (higher current flow through the voltage divider) negatively affect the measurement of the nanoampere signals?
    I am not sure, but it seems to me that a lower current through the divider gets me better detectable signals (higher amplitude in the scope). A first guess is that the current in the divider disrupts the ion current in the tube. On the other hand a higher overall impedance of a signal source is more susceptible.

    There are huge gaps in my knowledge about electrical engineering. Can you recommend literature to me? I read Plasma Chromatography, Ion mobility spectrometry and associated literature. When it comes to deeper physical questions I get lost for some reason.

    Talk soon

  2. jcsd
  3. Oct 3, 2014 #2
    Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
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