Marijuana breathalyzer breakthrough as scientists reveal ‘bomb sniffing’ technique that could lead to reliable roadside tests


While law enforcement officials can test for alcohol intoxication in a matter of seconds with the help of breathalyzers determining whether a person is under the influence of marijuana is far more complicated.

As weed is now legal across more than half of the US for medical or recreational use, scientists are working to develop the technology for roadside tests that measure the main psychoactive compound, THC.

In a new breakthrough, researchers tapped into bomb-sniffing technology to capture and analyze minute amounts of THC molecules in vapor, paving the way for accurate measurements of THC levels in the blood based on breath alone.

While driving under the influence of marijuana is universally illegal in the US, there are currently no practical ways to test for it if a person is pulled over.

Collecting blood or urine on site, for example, would be both impractical and invasive.

The scientists at the National Institute of Standards and Technology (NIST) investigated better ways to test for marijuana’s main psychoactive compound, delta-9 tetrahydrocannabinol (THC).

For the first time, they’ve managed to measure its vapor pressure, which has eluded researchers until now.

To do this, the researchers used technology called PLOT-cryo (porous layer open tubular cryogenic adsorption), which was invented by an NIST researcher back in 2009.

‘Vapor pressure describes how a compound behaves when it transitions from a liquid to a gas,’ said Tara Lovestead, a NIST chemical engineer and the lead author of the study.

‘That’s what happens in young lungs when a molecule leaves the blood to be exhaled in your breath.

‘So if you want to accurately measure blood levels based on breath, you need to know the vapour pressure.’

While molecules with high vapor pressure, such as ethyl alcohol, are constantly escaping as gas, the large, complex molecules of THC tend to stick together.



In their experiment, the researchers used PLOT-cryo to analyze THC molecules recovered from an inert gas.

PLOT-cryo has been used to sniff out explosive materials in airports, detect fire debris for evidence of arson, and even find hidden grave sites based on the faint scents of decomposition.

The team swept the gas across a sample of pure THC to capture any molecules that escape.

Then, they chilled the gas to collect these molecules.

Once they’d measured the mass of these molecules in a known volume and temperature of the sweep gas, they were able to calculate the vapor pressure.

They were also able to calculate the vapor pressure of cannabidiol, another less-psychoactive compound in marijuana.



PLOT-cryo has been used to sniff out explosive materials in airports, detect fire debris for evidence of arson, and even find hidden grave sites based on the faint scents of decomposition.

‘PLOT-cryo is an extremely sensitive technique for capturing and analyzing things in the vapour phase,’ Tom Bruno, NIST research chemist and co-author of the study, who invented PLOT-cryo.

‘It was a natural candidate for this type of problem.’

The work could pave the way for marijuana breathalyzers, the researchers say.

But, there’s still much research to be done before this can happen.

For now, scientists aren’t quite sure how breath levels of THC correlate to blood levels, and at what level a person becomes too impared to drive.

By obtaining accurate vapor pressure measurements, they’re hoping to achieve a consistent standard that could be used for the technology.

‘Fundamental measurements are the basis of standardization,’ Bruno said.

‘We’re laying the foundation for the reliable systems of the future.’


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