Compared to testing alcohol, checking for traces of cannabis compounds is exponentially more complicated. In the race to build a quick and reliable cannabis breathalyzer, scientists are looking to cutting-edge technologies in the fields of analytical chemistry and bomb detection.
Read on to understand how such new developments are influencing roadside testing methods for cannabis.
An instrument to sample vapor inside an old paint can, using PLOT-cryo (NIST photo)
A ground-breaking study, published by researchers from the National Institute of Standards and Technology (NIST), recommends using a unique testing method that leverages porous layer open tubular cryogenic (PLOT-cyro) absorption. PLOT-cyro was established in 2009 by Tom Bruno, a NIST chemist; which at the time was designed for detecting explosive substances and compounds at busy airports. Today, it is being utilized to support evidence for cases of arson.
Bruno believes PLOT-cryo could revolutionize cannabis testing by creating a foundation for standardization.
In cannabis detection, PLOT-cryo is capable of detecting THC on a molecular level. Unlike ethyl alcohol, THC compounds are difficult to measure because they possess very low vapor pressure. By comparison, high vapor pressure molecules are considerably lighter and escape more easily, making them easy to detect. Hence, traditional methods of roadside testing are not effective for cannabis. PLOT-cyro works by trapping THC compounds and analyzing the sample in the vapor phase.
“Vapor pressure describes how a compound behaves when it transitions from a liquid to a gas,” explained Tara Lovestead, a NIST chemical engineer and the lead author of the study, in a statement.
“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.”
Other scientists, from UC Berkeley and the University of Florida, are looking to ion mass spectrometry to improve success rates of cannabis breathalyzers. This method relies on filtering cannabis compounds using active particles. The process is very accurate, as it could tell researchers if the subject has consumed cannabis within a window of a few hours. However, it doesn’t provide data surrounding the amount of THC present in the subject’s bloodstream.
Classic Sobriety Test
The main issue with applying the same framework for alcohol testing is that both substances (alcohol and cannabis) differ greatly. An individual with high tolerance to cannabis could still function reliably after consuming large amounts; while a person with low tolerance may not be able to perform basic tasks, like driving, after a small dose. Because of this, using a breathalyzer device as a medium for cannabis detection may not generate accurate results.
“What matters is not the THC,” said Daniele Piomelli, a professor at the UC Irvine School of Medicine and an expert on cannabis. “What matters is if you are intoxicated.”
Piomelli suggests enforcing the classic behavioral field sobriety test as the main tool for detecting cannabis intoxication.
“There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment in the same manner we do alcohol,” said Marshall Doney, AAA’s president and CEO. “In the case of marijuana, this approach is flawed and not supported by scientific research.”
This post was originally published on July 21, 2017, it was updated on October 5, 2017.