Although several companies are working to develop marijuana breathalyzers, testing a person's breath for marijuana-derived compounds is far more complicated than testing for alcohol.
But scientists at the National Institute of Standards and Technology (NIST) have taken an important step toward that goal by measuring a fundamental physical property of the main psychoactive compound in marijuana, delta-9 tetrahydrocannabinol (THC). Specifically, they measured the vapor pressure of this compound—a measurement that, due to the compound's chemical structure, is very difficult and has not been accomplished before.
One reason it is difficult to design a reliable marijuana breathalyzer is that delta-9 tetrahydrocannabinol (THC), the primary psychoactive compound in marijuana, is a large molecule with a complex structure. Ethyl alcohol is more easily measured with a breathalyzer. In these images, carbon atoms are dark gray, hydrogen atoms are light gray, and oxygen atoms are red. 3D model based on computer rendering, not experimental data.
Credit: Kelly Irvine/NIST
• PLOT-cryo was used to measure the vapor pressures of CBD and Δ9-THC.
• PLOT-cryo stabilizes labile solutes because collection is done at low temperature.
• Vapor pressures were much lower than for compounds with similar molecular weights.