Gas chromatography is being applied on various fronts in the war against terror.

Homeland security involves protecting many locations from a variety of threats. Ports, borders, airports, subways, and buildings need to be defended from attacks by explosives or chemical and biological weapons. With this wide range of threats and locations, one might think that several separate technologies would be employed in order to detect all of the possible hazards.

Surprisingly, many of the different systems used to detect chemical weapons, biological weapons, and explosives are based on one technology: gas chromatography (GC).

"GC is used in both detection and early warning systems for homeland security," says Meredith Conoley, GC and GC/MS Products Commercial Sales Support Manager at Thermo Electron Corp., Waltham, Mass. GC is then combined with other technologies such as mass spectrometry (MS) to separate, analyze, and identify chemical, biological, and explosive compounds in samples from the air, water, and soil. "Mass spectrometry and other methods that provide more detailed information are used along with GC in order to identify specific chemicals," adds Conoley.

Detecting toxic substances
Gas chromatography/mass spectrometry (GC/MS) is used to detect and confirm the presence of toxic gases, explosive residues, and nerve gas metabolites. GC is used to separate the components of a mixture while MS characterizes each of the components individually. In this way, GC/MS is able to qualitatively and quantitatively evaluate a solution containing a number of toxic substances.

Many companies offer GC/MS devices that can be used to detect harmful agents. Shimadzu Scientific Instruments, Columbia, Md., combines their GC/MS system with a wide range of accessories and software to permit rapid identification of unknowns using commercial libraries. According to Bob Clifford, GC/GCMS Product Manager, Shimadzu's QP-2010 series GC/MS systems "enable users to perform accurate, high-speed identification and quantitation at low levels for a number of homeland security-related applications." These include the analysis of toxic substances such as cyanide, arsenic, poison gas, chemicals, and explosives.

GC/MS systems can also be used in environmental laboratories and municipal/industrial water plants, which have been increasingly mentioned as possible targets.

For their part, government agencies such as the National Institute for Standards and Technology (NIST), Gaithersburg, Md., use GC/MS to determime cyanide concentrations in human whole blood. This method has further been adapted by the Centers of Disease Control and Prevention (CDC), Atlanta, Ga., for transfer to state laboratories within the Chemical Counter-Terrorism Laboratory Network (CTLN), which includes laboratories in 46 states across the U.S.

Chemical agent detection is also being addressed with GC. Agilent Technologies, Palo Alto, Calif., in collaboration with the U.S. Army's Chemical Warfare program, has developed a GC-based chemical warfare agent detector. It is configured for both continuous, near-real-time monitoring and analysis of liquid samples.

In this device, GC is used to separate the samples, and then a photometric detector checks for sulfur- and phosphorous-containing chemical agents. A mass spectral detector (MSD) then provides structural confirmation of suspect agents. This system has already been used to detect and confirm the presence of nerve agents such as sarin gas as well as for blister agents such as mustard gas and nitrogen mustard.

Detecting biological threats
For their part, biological warfare agents, such as bacteria and viruses used to spread life-threatening diseases like anthrax, plague, and smallpox, are considered more deadly and accessible than their chemical counterparts. Agilent has teamed with MIDI, Inc., Newark, Del., to create the Sherlock Microbial Identification System, an automated GC-based system for detecting and identifying biological warfare agents.

The Sherlock system combines GC with fatty acid analysis to identify bacteria. Each strain of bacteria contains distinctive fatty acids in its outer membranes, which provides a unique fingerprint for each bacterium. The fatty acids are extracted to form fatty acid methyl esters (FAMEs) which are analyzed using GC. Pattern recognition software is then used to compare the unknown GC-FAME patterns to the MIDI libraries for the closest match. The Sherlock reference libraries consist of more than 2,000 entries and 25,000 analyses of strains obtained from experts and culture collections around the world.

Explosives detection is another area that is being improved with GC. The EGIS Defender, a portable lightweight desktop explosives trace detection system from Thermo Electron Corp., utilizes high-speed GC with Micro Differential Ion Mobility Spectrometry (HSGC-DMx) to detect plastic, commercial, and military explosives, improvised explosives, and nitrates.

The system works by first requiring its operator to collect samples by wiping a specially-designed wipe on the surfaces of objects, vehicles, or people. Once the sample is taken, the operator inserts the wipe into the sample inlet port on the instrument, which automatically initiates an analysis cycle. High-speed GC is used to separate explosives out of the sample. Once they are separated, DMx provides additional positive identification of trace amounts of explosive compounds down to the sub-nanogram level. This capability makes the EGIS Defender particularly useful for aviation screening, military access point control, border crossings, critical infrastructure, commercial and federal buildings including mail facilities, and at high-security events such as conventions and major sporting events.

Another explosives detection solution from Thermo is the EGIS II, which combines high-speed GC with chemiluminescence detection that only responds to nitrogen-based compounds. The samples are collected with sample wipes, as with the EGIS Defender. The sample is inserted into the device, and within 16 seconds, the detector display will appear red if explosives are detected and green if no explosives are detected.

Academic research

Academia has also stepped into the GC homeland security arena. An explosives detection device based on GC, pyrolysis, and ultraviolet (UV) detection (GC-PUD) has been developed by two chemical physicists at the California Institute of Technology (Caltech), Pasadena. This device directly detects the nitric oxide (NO) released from explosive compounds. Suspect samples are separated with GC, and the result is passed over a heated Nichrome wire. Any NO from explosive vapors will be released by pyrolysis when passing over the wire, and the NO can be identified by UV absorption spectroscopy. The specific type of explosive compound can be identified by the retention time in the GC.

At this point in time, the levels of explosives that are detected with this method are still higher than current commercial detectors. The Caltech researchers, J. L. Beauchamp and Robert Hodyss, believe that the sensitivity of this method can be increased by using a more sensitive UV spectrometer and improving the efficiency of the pyrolyser. Using a catalytic pyrolyser, which works at much lower temperature, will only produce NO from nitroorganic compounds, eliminating the potential problem of detecting NO from organic compounds containing both nitrogen and oxygen.

Other refinements are also in the works. "We have been working in the past few months to extend the methodology to other kinds of explosives, most notably TATP," explains Hodyss. "Our preliminary results suggest that we may be able to detect TATP with some minor modifications."

Taking it on the road
Most of the systems described above are laboratory-based. If a rapid response is required, mobile laboratories or field-transportable systems are necessary. One type of field-transportable system has been developed by Agilent. Their modular/flyaway laboratory can be packaged in boxes for transport with the durability to be dropped onto an incident site from a transport airplane.

A fully integrated self-contained lab on wheels is also offered by Agilent. Developed in conjunction with the U.S. military and ENG Mobile, Concord, Calif., the Agilent mobile laboratory contains separate, self-contained areas for sample preparation and sample analysis, and features Agilent GC-based systems for detecting biological and chemical agents.

Another portable solution, a wearable chemical and biological agent detector that uses GC/MS, has been developed for the U.S. Marine Corps by CyTerra Corp., Orlando, Fla. The CBIS (Chemical and Biological Individual Sampler) and Reader System combine to passively sample the surrounding air. The CBIS is a small device, about the size of a silver dollar, and can be worn for up to seven days. The Reader System is a high-speed analyzer that uses thermal desorption, fast GC and MS to analyze or "read" the CBIS and can complete the analysis in two minutes. Together, the CBIS and Reader System can provide early warning for sub-clinical levels of chemical or biological threats.

A GC-based handheld instrument for chemical and biological analysis has been developed by Sandia National Laboratories, Albuquerque, N.M. Named ┬ÁChemLab, it collects and concentrates samples, separates them using GC, and detects the constituent components using an array of surface acoustic wave (SAW) detectors.

The miniaturized GC columns are etched into a silicon wafer. All of the components of ┬ÁChemLab are mounted on a printed circuit board that carries both electrical and gas interconnects. Two complete analysis systems on the board allow parallel analysis of components under differing conditions, increasing the resolution. Analysis time from start to finish is seconds to minutes, with detection sensitivities of 10-100 ppb.

A similar GC-based chemical detection system that detects odors and chemical vapors produced by chemical and biological weapons, contraband of all kinds, hazardous industrial materials, improvised explosives, and flammable materials is already being used in ports to screen cargo containers and vehicles for contraband and explosives.

The zNose, developed by Electronic Sensor Technology, Inc., Newbury Park, Calif., recognizes odors and fragrances based upon their full chemical profile. GC is used to separate the chemicals, and a solid-state SAW sensor with electronically variable sensitivity identifies the chemical species in the vapor. The chemicals and their concentrations are determined within 10 sec with picogram sensitivity. "The zNose is being used at security checkpoints to screen for odors associated with both contraband and explosive devices, primarily by military force protection groups," says Thomas Ruschke of Electronic Sensor Technology. "Also, we have deployed six systems to Iraq where they are being used to help locate improvised explosive devices (IED) and their points of origin."

"Commercial companies have also discovered the zNose to insure physical security of products shipped in trucks and cargo containers," Ruschke adds.

Improvements to the zNose are ongoing. "Currently we are engaged in some exploratory studies using the zNose to detect non-nitrogen-based explosives such as TATP (human bombers) and toxic industrial compounds such as flammable liquids," explains Ruschke.

The future of GC in security
The need for homeland security will never wane. As the technology of the enemy gets more sophisticated, so too must the technology that is used to counter it.

"The most challenging problem is that of complexity," says Conoley.

"We want to prevent false positives and false negatives. GC systems will continue to have better sensitivity with more specificity, while at the same time getting smaller and having faster response times."

- Martha Walz