Hemp can look and smell like marijuana, presenting a series of challenges to law enforcement and farmers alike. But according to new research, lasers can be used to tell the difference between the two cannabis crops in a fast, affordable and highly precise way.
In a study published last month in the journal RSC Advances, a team of researchers at Texas A&M University were able to “determine whether plant material is hemp or [marijuana] with 100% accuracy” by using a hand-held laser device called a Raman spectrometer (RS).
To test whether the tool could effectively distinguish the two plants, fresh samples of hemp and marijuana strains were frozen, which, according to the authors, “does not result in any noticeable changes in plant appearance or texture.”
The researchers observed that lasers could reliably map a “change of intensities” in vibrational bands, which indicated “structural differences between hemp and [marijuana] plants.”
The results found that hemp has more cellulose, compared to marijuana plants.
“Because of the portable nature of our analysis, this spectroscopic approach will be highly advantageous for police and border control officers.”
The Raman spectrometer was also shown to potentially identify different strains by accurately measuring the potency of individual plants, which “can be used for confirmatory, non-invasive and non-destructive detection and identification of cannabis,” the authors wrote.
The researchers noted that their device detects delta-9-tetrahydrocannabinolic acid (THCA) which is itself non-psychoactive but turns into the intoxicating compound THC when it undergoes decarboxylation (usually by being heated). “[W]e can speculate that RS allows to predict the amount of THC in the analyzed sample without necessary oxidation of THCA to THC,” they wrote.
Additional laboratory testing is underway “to determine accuracy and range” of THCA prediction with the device.
Hemp is defined under federal law as having no more than 0.3 percent total THC, with a negligence threshold of 0.5 percent. And while there’s strong bipartisan interest in ensuring that hemp farmers have the resources they need following the crop’s federal legalization, proving that the plant isn’t marijuana currently requires costly and lengthy laboratory analysis.
“These results demonstrate that RS can be a great tool for hemp cultivation and breeding allowing for accurate detection of THCA levels in intact growing plants.”
With the right tools, officials could quickly determine whether a plant in question is hemp or marijuana, which remains prohibited federally and in several states.
In December, a Texas man was arrested when his vehicle was found hauling more than a ton of cannabis through Amarillo. The plants were seized, and the driver spent almost a month in jail before lab results showed he was transporting hemp.
Other similar discrepancies and mistakes are likely to keep occurring in states and municipalities across the country as new hemp laws come online.
Marijuana prosecutions in Texas were cut in half after hemp laws changed, for example, an unintentional side effect of expanding access to the non-intoxicating cannabis crop. Because police officers in many cases can’t determine whether a cannabis sample is legal hemp or illegal marijuana, prosecutors in the state and others across the country have stopped pursuing many cases until testing methods are more readily available.
The promising new laser technology could mean fewer headaches on the part of state and federal regulators—and a lower risk of getting tied up with law enforcement for law-abiding hemp traders.
“These findings suggest that a hand-held Raman spectrometer can be an ideal tool for police officers and hemp breeders to enable highly accurate diagnostics of THCA content in plants,” the researchers concluded.