Ion Mobility Spectrometry (IMS)
Collaboration between USDA-Agricultural Research Service and
Eiceman Group Laboratory, Department of Chemistry, New Mexico State University
An Ion Mobility Spectrometer is trace chemical detector that can detect and identify substances at very low concentrations in air at atmospheric pressure. Gas phase ions
are formed, admitted into an electric field, and separated by their time of travel.
IMS devices have been used for many years to protect soldiers from battlefield chemicals,
search for explosives at airports and screen for drugs at borders. This project adapts
IMS technology to find vapors from plastics contaminating raw seedcotton at the gin.
A military grade IMS (the Chemical Agent Monitor) demonstrates the utility
of IMS technology in rugged field conditions for life-critical applications.
Current research with modified IMS instruments detecting vapors from plastic and seedcotton
in a lab oven is discovering limits of detection and establishing neural network libraries.
Three boxes of electronics run the IMS, a fourth box contains the temperature controllers, and
a PCMCIA card in a PC provides the interface for instrument operation and spectra recording.
A collection of specta showing the differences with and without contaminating plastic.
Reactant ions form the large peak at left; product ions show up to its right.
Attempts to detect plastic contaminants in seed cotton are complicated by the volume and
velocity of conveying air (as much as 20,000 cfm at up to 68 miles per hour). Here off-
the shelf IMS instruments are tested at the USDA-ARS Southwestern Cotton Ginning Research Lab.
Earlier work with Gas Chromatography (GC) separated molecules by size before sampling with IMS.
This increased resolution but was too slow to achieve desired on-line contamination detection.
Earlier work with off-the-shelf IMS instruments designed for other applications confirmed that
plastic vapors can be detected, and that custom instrumentation is necessary for this application.
Three generations of IMS design illustrate reduction in size (and cost) from miniaturization.
Commercial devices are now available from:
Smiths Detection
and
Sionex Corporation
for certain applications.