Ion Mobility Spectrometry (IMS)

Ion Mobility Spectrometry is the science behind our world-leading range of chemical agent detectors and explosives detectors.

Ion Mobility Spectrometry (IMS) is an atmospheric pressure chemical detection technology that is, in many ways, similar to Time-of-Flight Mass Spectrometry. IMS provides an unrivalled combination of detection features:

Through this powerful combination of features, IMS based systems have found extensive use in many diverse areas, from common applications such as detection and monitoring of chemical warfare agents (CWAs) and toxic industrial chemicals (TICs) in the military arena or detection of explosive traces on luggage in airports, to monitoring the atmosphere inside the International Space Station (ISS).

Principle of Operation

A schematic diagram of Ion Mobility Spectrometer is shown below.

IMS uses soft ionization techniques, such as 63Ni or corona discharge, to form reactant ion species from the carrier gas employed in the system, normally air. Mixing these stable reactant ion clusters with vapor samples to be analyzed can result in ionization of the sampled materials, thus forming ion clusters characteristic of the sample material. This ionization process is generally referred to as Atmospheric Pressure Chemical Ionization (APCI).

A small packet of the ions so formed is injected electrically into a drift region, where they pass to a collector electrode some distance away (typically a few cm) under the influence of an applied electrostatic field. Ions travel through the drift region at characteristic speeds that are related to the size and shape of the ion clusters.

On arrival at the collector, each ion species generates a specific signal, and the ion current as a function of arrival time is measured. Ion Mobility (K) is determined from the drift velocity (vd) attained by ions in a weak electric field (E) in the drift tube, according to the simple equation, v­d = K x E. A plot of ion current against K forms an ion mobility spectrum, with an ion mobility band corresponding to each of the unique ionic species. The spectrum is a fingerprint of the parent compound.

The measured IMS spectrum is analyzed and mobility information is extracted in real time within the instrument. Comparison of measured motilities with the known nobilities of threat compounds will give rise to an ALARM condition if there is a match.