GAS BreathSpec, User Manual

Page: 29 / 242

BreathSpec®
– User Manual
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5 Introduction
5.1 Working principle of IMS technologie
Ion Mobility Spectrometry (IMS) is an analytical technology to separately detect
gaseous compounds in a mixture of analytes. The separation is based on the specific
drift times, that ionized compounds need to pass a fixed distance (drift tube) in a
defined electric field.
Figure 1: Ion Mobility Spectrometer - Basic Relations
Compared to other techniques e.g. TOF-MS, ions travel at atmospheric pressure
versus a flow of inert drift gas. The drift time of each substance is determined by its
ion mass and geometric structure, as slowing collisions with the drift gas molecules
are more frequent for sterically demanding structures. Therefore, IMS can even
differentiate isomeric molecules. For detection, the resulting ion current is measured
by an electrometer as a function of time.