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.
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.
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.
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
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
“It’s not either
or,” Verkouteren said. “You want a variety of tools in the toolbox.”
Rich Press is
science writer and public affairs specialist with the National Institute of Standards
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.