Programmable ion mobility spectrometer: Time resolution improvement and ion counter comparison

Atmospheric ion mobility spectrometers operating on the aspirated electrode principle require switching of a bias voltage to select ions of different mobility. The ion spectrum can be obtained by sweeping across a set of bias voltages. If rapid temporal changes in atmospheric ion spectra are to be m...

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Bibliographic Details
Published in:Review of scientific instruments 2005-08, Vol.76 (8), p.086109-086109-3
Main Authors: Harrison, R. G., Wilding, R. J.
Format: Article
Language:English
Subjects:
AIR
AMPLIFIERS
BALLOONS
CAPACITANCE
ELECTRIC POTENTIAL
ELECTRODES
ELECTROMETERS
HOURLY VARIATIONS
INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY
ION MOBILITY
IONIZATION
MASS SPECTROMETERS
SPECTRA
TIME RESOLUTION
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Summary:Atmospheric ion mobility spectrometers operating on the aspirated electrode principle require switching of a bias voltage to select ions of different mobility. The ion spectrum can be obtained by sweeping across a set of bias voltages. If rapid temporal changes in atmospheric ion spectra are to be measured, however, such as for a balloon-carried instrument, the sweep time across the ion spectrum must be kept short. As bias voltage steps can generate saturation in the mobility spectrometer's electrometer amplifier, the electrometer recovery time limits the ion mobility spectrum sweep rate. Here, active compensation of the charge injected at a bias voltage step is used to reduce the saturation time. Further, the optimal setting of the charge compensation circuitry provides a determination of the system capacitance, a necessary calibration parameter for absolute measurements. Using laboratory air, hourly variations in ion concentrations and air conductivity found using the voltage switching system were similar to those obtained with a traditional ion counter operating at a single mobility: ion growth, however, could only be detected using the ion spectrometer.
ISSN:0034-6748
1089-7623
DOI:10.1063/1.2010469