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It’s pretty easy to single out a driver that is driving under the influence of alcohol. Swerving between lanes, running red lights and inconsistent speed are signs easily identifiable to passersby and police alike. Additionally, police can conduct a test using a breathalyzer to estimate the amount of blood alcohol content in said driver—providing unequivocal confirmation of the presence of alcohol.

But how do you spot a driver who is driving “high,” or under the influence of marijuana? He or she could be showing signs similar to a drunk driver, but not necessarily since the effects of marijuana in large doses are much different than the effects of alcohol.

Each state has its own laws regarding the blood alcohol level of drivers in terms of what is considered legal and what is considered legally drunk, or under the influence. And now, with more states legalizing both medical and recreational marijuana, legal limits are being set in this arena as well.

However, they are not as clear as drunk driving laws—which is more a function of the vice than the law itself.

Unlike alcohol, THC—the active compound in marijuana that leads to a high—can stay in a user’s blood for minutes, days, hours or even months depending on what strain of marijuana is used, how often, and the specific method of ingestion.

For example, a standard blood test can detect 1 to 2 ng/mL THC in the blood of a chronic user for two days, and an occasional user for eight hours. This is upped significantly if the user ingests marijuana through an edible, like a gummy bear or chocolate.

In Colorado, the legal limit is 5 ng/mL, so the chronic marijuana user who last ingested the plant two days ago would be fine. However, in a “zero tolerance” state like Rhode Island, the user would find himself arrested and behind bars—even if s/he isn’t high because their last marijuana ingestion was two days ago.

“There are just so many questions we need to address, and so much we don’t know,” said Tara Lovestead, a chemical engineer at NIST. “The biggest issue for law enforcement is Δ9-THC in the blood does not correspond to intoxication.”

At the Forensics@NIST conference in November, Lovestead gave a presentation describing her work to identify other chemical markers indicative of marijuana intoxication. She is focusing on creating noninvasive, portable breath tests for Δ9-THC that can indicate recent marijuana usage from 30 minutes to 2 hours prior.

Lovestead said her team’s approach incorporates three key areas: fundamental data; materials development; and “breathalomics.”  

Chemistry-wise, there is still a lot researchers do not know about cannabis, THC and other cannabinoids. So, part of Lovestead’s research is to research. Her and her team are measuring vapor pressure, molecular interactions and partition co-efficients to successfully apply it to overall cannabis research.

They are also researching and/or developing new materials to outfit a potential marijuana breathalyzer device, especially in terms of what is best suited to crucial absorption and desorption techniques.

Last, but certainly not least, Lovestead is paving a way toward determining the chemical signature of marijuana intoxication.

To do so, Lovestead has thus far relied on a dynamic headspace sampling technique called porous layer open tubular (PLOT)-cryoadsorption that has provided extremely sensitive quantitative recovery of Δ9-THC. The method highly decreases the amount of time expended to identify vapor pressure information.

Another method Lovestead uses for breath collection is capillary microextraction of volatiles. Unlike PLOT-cryo, this method is already ready for in-the-field sampling, and is most suited for the breath collection of cannabis-related metabolites, which indicate if a user actually smoked marijuana or just ingested it secondhand.

“[Fundamental data, materials development and breathalomics] build upon one other and help the other out,” Lovestead said about her lab’s approach to a marijuana breath test. “In the future, we are going to look at more artificial breath work with the different materials available.”

See Lovestead's entire presentation here (Day1, Part 4), along with her slides.

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