Tracing A Threat With hopes of thwarting and even deterring a chemical attack, scientists search for the fingerprints of potential threat agents
By Bethany Halford
Everything leaves a trace—fingerprints, ballistics, DNA. Law enforcement agents have an extensive forensic toolbox to link perpetrators to crime scenes and murder weapons. But what happens when the murder weapon is a molecule? Scientists are discovering that even a chemical holds clues that can point to its source.
This nascent field is known as chemical forensics. Its goal is to take analytical techniques that have been used for forensic analysis, such as impurity profiling and stable isotope analysis, and use them to attribute weaponized toxic chemicals or related substances to their sources. A chemical forensic analysis could, for example, trace a chemical threat agent back to the specific lot of the precursor that was used to make it.
By developing chemical forensics, scientists “have a greater chance of finding perpetrators of chemical attacks or their sources of materials before they can strike again,” explains Carlos G. Fraga, a chemical forensics expert at Pacific Northwest National Laboratory (PNNL).
Scientists are also using impurity profiling to differentiate routes used to purify the deadly protein ricin (bottom left), which comes from castor seeds (bottom right). David S. Wunschel (top photo) and colleagues at PNNL prepared ricin by four methods—three from kitchen recipes that appear in “anarchist literature” and one from a relatively simple laboratory procedure. They made derivatives of the carbohydrates and fatty acids found with the ricin, analyzed them by GC/MS, and were able to differentiate among the preparations used to go from seed to protein (Anal. Chem., DOI: 10.1021/ac1006206).
As components are stripped from the seed, the material is going to change, Wunschel explains. For example, castor oil accounts for roughly half of the contents of the castor seed, and the fatty acid ricinoleic acid accounts for a large portion of that oil. If someone were to try to isolate ricin, they’d first want to strip away that oil, resulting in a loss of ricinoleic acid. Wunschel and his coworkers found that ricinoleic acid levels will vary depending on the purification method and how well someone succeeds in purifying the protein.
“You’re likely to remove seed components that have different carbohydrate markers,” Wunschel adds. Specifically, he and his colleagues found changes in arabinose and mannose concentrations after precipitation of the ricin protein. These carbohydrates originate in the castor seed’s cell wall. Some are lost and some are enriched depending on how the ricin was isolated.
“Just being in possession of castor seeds is not a crime,” Wunschel points out. But applying this sort of analysis to residues found in some clandestine lab could reveal whether someone was trying to extract oil or remove cell wall components in an attempt to purify ricin, he says.