NIST Tests Performance of Screening Device for Detecting Fentanyl at Border Crossings
Written by Rich Press   

LARGE QUANTITIES OF FENTANYL and fentanyl analogs are entering the country at ports of entry along the southwestern border of the United States, according to the Drug Enforcement Agency. Law enforcement agencies are considering chemical screening devices that might help stem the flow.


Now, scientists at the National Institute of Standards and Technology (NIST) have tested the performance of ion mobility spectrometry (IMS) when used to screen vehicles for fentanyl. Their results, recently published in the journal Analyst, include sensitivity levels, error rates, and other metrics that can help authorities weigh the costs and benefits of this technology.

IMS is already deployed at airports to screen for explosives and at prisons to screen for narcotics. But the performance of IMS varies depending on the substances being targeted and the chemical environment where the screening takes place. This research is the first to test the ability of IMS to distinguish trace amounts of fentanyl from the potentially confounding compounds that might be present at a border crossing.

The researchers conducted their tests at the loading dock of a federal facility. Because this test site is full of vehicles and cargo, it is likely to have a chemical environment similar to that of a border crossing. Security officers at the loading dock use IMS instruments to screen vehicles entering the facility for explosives. To do this, they swab steering wheels, door handles, and other surfaces, then test the swabs for explosive residues.

Most IMS instruments can be configured to record a history of data from past tests. This logging feature was enabled at the loading dock, which provided the researchers with a convenient archive of the chemical signals the instruments had encountered in the past. The logged data did not include any obvious signals indicating the presence of fentanyl or fentanyl-related compounds.

To see what the data would look like if the instruments had encountered fentanyl or related compounds, the researchers treated swabs with drugs in amounts varying from single nanograms up to 100 nanograms, then ran those swabs through the instruments. They ran these tests using fentanyl, 12 fentanyl analogs, heroin, and U-47700.

“We found plenty of background clutter in that environment, but the amount is generally low enough that the signal from the drugs comes through clearly, even at trace levels,” said Thomas Forbes, a NIST scientist and lead author of the study.

An IMS instrument does not produce conclusive results. It is a screening device that indicates whether a vehicle should be searched. If a search does turn up something suspicious, further tests would be needed to confirm which, if any, drugs are present. In addition, IMS might not be able to distinguish between a vehicle being driven by a drug user and one that is smuggling bulk quantities of illegal drugs. Again, a search would be needed.

Unnecessary searches would slow border operations and negatively impact innocent drivers, so the number of false positives needs to be managed. The researchers used a statistical technique called receiver operating characteristic (ROC) curves to estimate the false positive error rates that would be expected at their study site. Their calculations showed that, if the instruments at that site were configured to detect trace amounts of the drugs in the ten nanogram range, they would have achieved a two percent false positive error rate (two percent of positive results would be false). The expected error rates at that sensitivity varied slightly from one drug to the next.

Most of the fentanyl being trafficked across the southwestern U.S. border is mixed with other drugs and bulking agents. Prior research by NIST has shown that IMS instruments can detect trace amounts of fentanyl even when it is adulterated in this way.

The IMS instruments at the loading dock were specifically designed to detect explosives, but manufacturers sell other models designed to detect narcotics. The NIST researchers found that narcotics-specific instruments were about ten times more sensitive to the drugs than the explosives instruments, but the explosives instruments were sensitive enough for screening purposes. Therefore, if agencies already have an inventory of IMS instruments designed to detect explosives, they can potentially be repurposed for use at the border.

Because the loading dock has a slightly different chemical environment than border crossings, the performance of IMS at the border would differ slightly from the results achieved in this study. However, the authors demonstrate how to use ROC curves to calculate expected error rates and sensitivity levels at a given site based on logged IMS data from that site. “This study provides a roadmap for getting a customized analysis for your particular environment,” said NIST scientist and coauthor Jennifer Verkouteren.

Border agents already screen vehicles with a different type of chemical sensor that is among the most sensitive known to modern science. So why also use IMS? Because dogs have to take frequent breaks and can be killed if they inhale fentanyl directly.

“It’s not either or,” Verkouteren said. “You want a variety of tools in the toolbox.”

About the Author
Rich Press is science writer and public affairs specialist with the National Institute of Standards and Technology.

Forbes,T, J. Lawrence, J. Verkouteren, & R.M. Verkouteren. Discriminative potential of ion mobility spectrometry for the detection of fentanyl and fentanyl analogues relative to confounding environmental interferents. Analyst. Published online Sept. 27, 2019. DOI: 10.1039/c9an01771b.

This article appeared in the January-February 2020 issue of Evidence Technology Magazine.
You can view that issue here.

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