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Chemical/Gas

Portable Chemical Profiling

February 1, 2006 By: Edward J. Staples Sensors

Electronic noses can play a major role in preventing unwelcome—or dangerous—cargo from entering our ports. The same technology could make buildings, subways, airports, and other public spaces safer as well.


The U.S. now inspects 4% of the 6 million shipments arriving at more than 100 ports; before the September 11, 2001, attacks that figure was 2%. About 20% of the cargo passes through overseas ports such as Hong Kong, where U.S. inspectors are being stationed. Cargo worth $1.2 trillion, or half of U.S. imports, arrives by sea. The rest comes in from Canada and Mexico. Given the sheer volume of arriving merchandise, there is a good chance that some shipments will include unwelcome items. But how can they be discovered—and identified—without a lengthy inspection of every container?



Current sensor capabilities are fairly limited; in many cases, the best "technology" for practical use continues to be trained "sniffer" dogs. Manufactured sensors are often designed for use in specific environments, and to be selective for only one or two chemicals. The spectrum of potential threats, however, argues for sensor systems capable of detecting a large variety of chemicals. In addition, sensor systems need a number of different subsystems, including sample collection and processing, presentation of the chemicals to the sensor, and sensor arrays with molecular recognition.

In this article we present an electronic nose called the zNose that uses a single solid-state sensor to create an unlimited number of specific virtual chemical sensors for chemically profiling odors in cargo containers. Virtual sensor arrays and recognizable olfactory images for explosives, hazardous substances, illicit drugs, and even the cargo itself can provide a cost-effective screening tool for shippers and inspectors alike.

In support of container security protocols, odor profiles can also be attached to an electronic manifest file and forwarded to authorities at the country of destination for comparison purposes.

Chemical Profiling with High-Speed GC

A portable chemical profiling system (Figure 1) incorporating an ultra-high-speed gas chromatography (GC) column, a solid-state sensor, a programmable gate array microprocessor, and an integrated vapor preconcentrator is able to speciate and quantify the vapor chemistry within a cargo container in 10 s.

Figure 1. Portable chemical profiling system incorporating an ultra-high–speed gas chromatograph
Figure 1. Portable chemical profiling system incorporating an ultra-high–speed gas chromatograph

Vapors within the container are sampled by inserting a sampling tube attached to the inlet of the instrument through a small opening in the container door, or through the ventilation ducts of the container (Figure 2).

Figure 2. Vapors are sampled by inserting a probe attached to the inlet of the instrument into a small resealable hole in the container
Figure 2. Vapors are sampled by inserting a probe attached to the inlet of the instrument into a small resealable hole in the container

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