Scientists have been working towards creating a marijuana breathalyzer, allowing authorities to determine cognitive and behavioral impairment. Delta-9-tetrahydrocannabinol (THC) is a large molecule with a complex structure compared to ethyl alcohol, making the development of a product like this very challenging. The goal is to measure the vapor pressure of THC.
With the legalization of recreational and medical marijuana in 30 states, authorities are trying to keep the public safe and prevent people from driving under the influence of marijuana. To be able to enforce this, a roadside test for marijuana intoxication needs to be implemented.
Scientists at the National Institute if Standards and Technology (NIST) have discovered how to measure a fundamental physical property in marijuana. A chemical engineer from NIST explains how this can be accomplished, “Vapor pressure describes how a compound behaves when it transitions from a liquid to a gas. That’s what happens in your 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 vapor pressure.”
Compounds with high vapor pressure such as ethyl alcohol, constantly escape into the vapor phase, while compounds with low vapor pressure such as THC that have large complex molecules, escape slowly. A new technique had to be created to apply technology that can measure the vapor pressure and have a quick and accurate response. It’s called PLOT-cryo (Porous layer open tubular cryogenic absorption). This technology was invented in 2009 to use with airport puffer machines. This highly sensitive machine can capture and analyze the few molecules of THC that do escape into the vapor phase.
Along with being able to measure THC, it can capture the compound cannabidiol. The study was performed by, “sweeping an inert gas across the sample of pure THC to capture escaping molecules, then chilled the gas to collect them (that’s where the ‘cyro’ part of the name comes from). By measuring the mass of the recovered molecules in a known volume and temperature of sweep gas, the researchers calculated the vapor pressure.”
Scientists need to look at multiple variables while conducting research, for example, how do the levels of THC impact people when its consumed or inhaled. Another challenge they face is that THC leaves the bloodstream quicker than alcohol, the impairment of the user last several hours longer than THC concentrations stay in the blood stream. It also accumulates in the tissues; the slow release can show positive in a test several weeks later. Marilyn Huestis from the National Institute on Drug Abuse states, “…on average in the United States it takes from 1.4-4 hours after a crash or traffic stop to administer a blood test. If someone is driving impaired, by the time you get their blood samples, you’ve lost 90% or more of the drug.” This is also posing a problem with how quick THC can leave the bloodstream. Changing the test performed at the roadside when the individual is most impaired could make a difference in keeping the public safe and impaired drivers off the road.
Further research needs to be conducted to understand how breath levels of THC correlate with blood levels, and how that correlates to levels of impairment. Along with the possibility of creating a device to assist authorities, they also need to be trained on how to identify behavioral signs of impairment.