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Impurity profiling and stable isotope analysis: an exploration of techniques used to trace the origins of chemical warfare agents.

The perpetrator of a crime always brings something to the crime scene and always leaves with something from it. This is known as Locard's exchange principle, and it is the basis of several forensic science subdisciplines (such as fingerprint, deoxyribonucleic acid [DNA], serology, hair and fiber, ballistics, and tool mark analyses).

How do we find the perpetrator when a chemical warfare agent is used as the murder weapon? Under Locard's principle, the chemicals or the delivery mechanism--two things that were brought to the crime scene--can point to the responsible party. In reality, the responsible party is likely an entire network of actors of concern. According to the Department of Defense Strategy for Countering Weapons of Mass Destruction, actors of concern are any state or nonstate actors that carry out activities that pose a clear and potential threat to the U.S. government. (1) In the context of weapons of mass destruction (WMD), actors of concern may be involved in developing, acquiring, proliferating, or employing WMD-related expertise, materials, technologies, or means of delivery. Through the field of chemical forensics, we are discovering that two well-established analytical methods (impurity profiling and stable isotope analysis) can lead investigators back through the network to the actors of concern who are responsible.

By tracing the components and impurities of a chemical warfare agent to the specific lot of precursors used to make it, investigators may be able to find answers to many important questions. Where did the precursors come from, and who paid for them? Where were the precursors delivered and by whom? What type of equipment was used during production? What methods or laboratory processes were used during production, and does this point to a group of well-educated scientists or a single self-taught terrorist? Where did the funding for the chemical agent production come from? And most importantly: Were additional chemical weapons produced--and, if so, where are the chemical weapons now?

The key to tracing and countering potential threats lies in identifying the impurity profile of a chemical agent and conducting a stable isotope analysis. A chemical impurity is any chemical substance that is present with another chemical substance and differs in chemical composition. (2) Impurities can occur naturally, or they can be introduced during the synthesis of a product. Depending on the desired product, impurities can be intentionally or unintentionally added; but in the case of chemical warfare agents, the more pure the final product, the more lethal it is. In pharmaceutical research and forensic science, impurity profiles are typically obtained using high-performance liquid chromatography, gas chromatography, mass spectrometry, or nuclear magnetic resonance spectrometry. (3)

Impurity profiling has been a valuable tool for chemical forensics for many years. Crime scenes present a variety of conditions and environments in which impurities can be introduced into samples (drugs, body fluids, explosives, paint) recovered for forensic analysis. For instance, the process by which drugs (cocaine, heroin) are processed introduces many impurities from the various substances or methods used by the production line to increase the overall yield. These impurities add forensic value to the products because the impurities make the product more unique, thus improving the ability to match or trace the drugs in the future.

The Department of Homeland Security Chemical Forensics Program is leading the way in developing and maintaining expertise in collecting, preserving, and forensically analyzing chemical warfare agents. The Chemical Forensics Program is developing technology and analytical techniques specific to chemical warfare agent investigations to trace and possibly counter future threats. The key lies in identifying a chemical agent impurity profile and stable isotopes. The two features, when identified individually or in tandem, make up what is known as a chemical attribution signature. Chemical attribution signatures are identifiable features that are inherently valuable in associating various samples with each other and distinguishing how, where, or by whom the recovered samples were produced and subsequently handled.

The Chemical Forensics Program is focused on four main areas of research:

* Determining if high-priority chemical agents produced by various synthesis methods or procured from various commercial sources contain or retain specific chemical attribution signatures.

* Determining environmental factors or effects that can alter chemical attribution signatures and affect recoverability.

* Developing techniques and tools for sampling different types of chemical attribution signatures at chemical incident scenes, with emphasis on stabilizing the samples and minimizing degradation.

* Developing optimal methods and analytical techniques for conducting comprehensive forensic analyses of samples for source determination and association with other samples.

Building upon these focus areas, the Department of Homeland Security is increasing national preparedness when responding to incidents and providing investigators with a forensic means to locate perpetrators and prevent future attacks.

Many organizations are currently using impurity profiling to track illegal drugs. The U.S. Drug Enforcement Agency might use impurity profiling on drugs that have been seized before sending them back into circulation to determine dealer-user relationships, distribution networks, and drug sources. This technique can also be used to track counterfeit pharmaceuticals, banned pesticides, and homemade explosives.

In the context of forensics, stable isotope analysis refers to the comparison of the distinguishing combination of stable isotope abundances of different elements present in a given sample to a suspected source in an effort to determine the origin of the sample--possibly tying a sample to a specific person, location, or source material. The terms isotope fingerprint and stable isotope signature are used to describe the tangible combination of isotopes that have value in attribution to a source, but it is important to remember that stable isotope fingerprints and signatures can change over time. (4) For instance, the isotopic composition of sarin or soman nerve agents can change as the more volatile components in the mixture evaporate and are lost to the atmosphere. However, if background information (such as a database of isotopic signatures for nerve agent precursors at the time of their manufacture) exists for the material in question, it may be possible to draw conclusions regarding the expected changes in isotopic composition based on known storage conditions or environmental exposures.

Dr. Carlos Fraga, a chemist from the Pacific Northwest National Laboratory, developed the impurity profiling technique for tracing residual contamination left by chemical attacks to the source where the precursors were obtained. The impurities in a chemical warfare agent can be matched to the impurities in the precursor chemicals, which point back to the likely source. The impurities are highly unique to the precursor batch, much in the same way that fingerprints are unique to individuals. Dr. Fraga's research also found that up to 88 percent of the impurities found in the precursors can still be identified in the final product even after a distillation and two solvent extracts.

Current methodologies limit the forensic application of impurity profiling and stable isotope analysis to laboratories with strict quality assurance/quality control measures and the necessary equipment to perform sample preparation and analysis. Future research, however, must explore the development of a field-deployable instrument to provide real-time information to military chemical exploitation units.

Currently, specialized military units are able to sample and perform presumptive or field confirmatory analysis to help higher echelons of command make informed decisions on the battlefield. The current technology can be used to analyze samples of chemical warfare agents, precursors, and toxic industrial materials to provide the Soldieroperator with the chemical composition of the sampled material. Such information can help ground units identify the agents that are being produced based on the ingredients present at the site and other visible intelligence (documents, laboratory equipment). By knowing which agents are in production and the current stage of the process for the actors of concern, the military team can make informed decisions regarding the personal protective equipment necessary to continue the mission and the mitigation steps necessary to destroy or further exploit the site.

Current technology falls short of the ability to link synthesized chemical warfare agents or the precursors within the agent to the specific precursor batch and its origin. The addition of such a capability would allow exploitation teams to provide immediate information to intelligence assets that could begin the process of identifying more actors of concern within the WMD network. The quicker the intelligence picture grows, the faster ground units can undertake tactical missions to prevent the acquisition of the materials, contain WMD threats, interdict the transit of weapons or materials, safeguard the force, and conduct consequence management operations. These specific measures designed to counter the proliferation of WMD materials would decrease the time it would take to identify those responsible, thus preventing the potential loss of lives and ending conflicts more quickly.

Such technology, however, would rely on an immense, ever-growing database. It would not be possible to rely on an internal library because of the continuous manufacturing of chemicals. The equipment would require a secure satellite link to a database containing every chemical warfare agent threat precursor in global circulation--complete with its impurity profile and stable isotopic signature, which would need to be entered into the database at the time of its manufacture by the chemical production company. However, the database cannot account for environmental conditions, exposures, and storage conditions that the material goes through after leaving the factory. These conditions can alter the original impurity profile and isotope signature. For this reason, a field-deployable instrument, like many others in the gamut of military chemical detection equipment, may be plagued by false-positives, false-negatives, or inconclusive results.

Due to the ongoing risk of chemical attacks, a forensic technique to quickly identify the presence of chemical warfare agents and trace their origin is of great interest when countering the proliferation of WMD. On a national strategic level, these forensic advances help fulfill two priority objectives outlined in the Department of Defense Strategy for Countering Weapons of Mass Destruction: (5)

* Reduce incentives to pursue, possess, and employ WMD.

* Increase barriers to the acquisition, proliferation, and use of WMD.

The ability to effectively trace chemical weapon origins serves as a deterrent to the use of chemical weapons due to the possibility of targeting perpetrators and defeating their network. Decreasing the appeal of WMD has caused actors of concern to be less likely to pursue, possess, or employ WMD; and defeating the network has caused barriers to the acquisition, proliferation, and use of WMD to be increased.


(1) Department of Defense Strategy for Countering Weapons of Mass Destruction, June 2014, <http:// /DoD_Strategy_for_Countering_Weapons _of_Mass_Destruction_dated_June_2014 .pdf>, accessed on 6 October 2015.

(2) Title 40, Code of Federal Regulations, Section 720.3, Definitions, June 2014, < /text/40/720.3>, accessed on 21 October 2015.

(3) Nikolaos Grekas, Organic Impurities in Chemical Drug Substances, Pharmaceutical Technology Europe, October 2005, < -drug-substances>, accessed on 21 October 2015.

(4) W. Meier-Augenstein and H. F. Kemp, 'Wiley Encyclopedia of Forensic Science," Stable Isotope Analysis: General Principles and Limitations, 2012, pp. 7-8, <http://www.academia .edu/1500626/Stable_Isotope_Analysis_General _Principles_and_Limitations>, accessed on 21 October 2015.

(5) Department of Defense Strategy for Countering Weapons of Mass Destruction.


John Fischer, Chemical Forensics ProgramProviding Law Enforcement with New Forensic Tools for the Investigation of Chemical Attacks, U.S. Department of Homeland Security Science and Technology Directorate, 31 October 2014, < /files/publications/Chemical%20Forensics%20Program -Providing%20Law%20Enforcement%20with %20New%20Forensic%20Tools%20for%20the %20Investigation%20of%20Chemical%20Attacks.pdf>, accessed on 6 October 2015.

Bethany Halford, "Tracing a Threat," Chemical and Engineering News, Volume 90, Issue 6, 6 February 2012, <http://>, accessed on 6 October 2015.

Douglas Page, "Amazing Trace," Forensic Magazine, 18 June 2012, < -trace>, accessed on 6 October 2015.

By Captain Spencer R. Roberts

Captain Roberts is the deputy director, Personnel Recovery Cell, 4th Infantry Division, Fort Carson, Colorado. He holds a bachelor's degree in anthropology from the University of Tennessee, Knoxville, Tennessee, and a master's degree in forensic science from the University of Florida, Gainesville, Florida.
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Author:Roberts, Spencer R.
Publication:CML Army Chemical Review
Date:Dec 22, 2015
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