- #1
Flowaone
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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
Florian
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
Florian