Ion Mobility Spectrometry (IMS) is an analytical technique that detects gaseous compounds on the basis of their ion mobility. That is, it measures the time needed for the ions of these compounds to drift through an electric field at ambient pressure and temperature. The technique is very fast, sensitive and often ideal for detecting very low levels of compounds or when analysis is needed in the field rather than a laboratory.

The typical ion mobility spectrometer contains four basic components: an inlet system, an ionization chamber, a drift tube and a detector. The sample being analyzed must be in a gaseous state, either naturally or through an appropriate sample preparation technique. After the sample enters the inlet, it is exposed to the ionization source, forming either positive or negative ions. These ions then pass through a shutter that controls the passage of ions in the drift tube.

Inside the drift tube is an electric field and neutral drift gas which separates the ions according to their mobility. High vacuums are not required in this process as they typically are for other MS techniques, thus making these instruments less expensive to construct and better able to miniaturize.

When a gaseous ion from the sample is exposed to a constant electric field at atmospheric pressure, it accelerates until colliding with a neutral molecule. Upon collision, the ion slows down, but the electric field accelerates it again. These collisions repeat until the ion reaches the detector, with the pattern of deceleration and acceleration at the molecular level translating into a constant ion velocity over macroscopic distances. The time it takes for an ion to reach the detector depends on several factors, including the geometric shape, mass and charge of the particle. The resulting ion current is measured by an electrometer as a function of time. The energy gained from the electric field is randomized by ion collisions, and the combination of acceleration and collision results in a constant average ion velocity that is directly proportional to the electric field. The ratio of ion velocity to the magnitude of the electric field is called ion mobility.

IMS technology is ideal for the detection of explosives, narcotics and chemical warfare agents, and is therefore a well-established technique for military and security applications. In fact, IMS is still the main technique used to analyze chemical warfare agents. In recent years, new applications for IMS have been developed as well, including air quality analysis, process control, medical diagnostics and proteomics analysis.

In 2016, the total IMS market was about $330 million, with most sales being attributable to portable or handheld models. Top suppliers of the technology last year included Bruker, Morpho Detection, Nuctech and Smiths Detection. As part of the agreement for the acquisition of Morpho Detection by Smiths in April 2017, the IMS technology formerly owned by Morpho Detection is in the process of being sold to OSI Systems.

While the market for IMS is largely mature for security functions, new applications that involve coupling the technology to mass spectrometry or chromatography systems are showing promise for niche applications, particularly in other functions such as life science research, environmental testing and forensics.

IMS at a Glance:

Leading Suppliers:

• Smiths Detection
• Bruker
• OSI Systems (pending purchase of Morpho Detection IMS)

Largest Markets: 

• Government
• Environmental Labs
• Transportation/Shipping

Instrument Cost:

• $10,000–$100,000