Safeguarding Against Terror With GC
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 µChemLab, 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 µChemLab 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
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