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I'm Nabil Saad and I'm a senior applications scientist at Picarro. I'll be blogging periodically about applications development around stable isotopes. There is a lot going on. So last month we delivered a brand new Picarro Combustion Module-Cavity Ring-Down Spectrometer (CM-CRDS) to the U.S. Customs and Borders Protection (CBP), which is part of the Department of Homeland Security. The initial purpose of the CM-CRDS was to smoke marijuana. No, really. Our friends over at Customs plan to combust seized marijuana in Picarro’s combustion module and study the stable carbon isotope ratio of the cannabis using the coupled CRDS analyzer, This will be done automatically with a click of a button and take only a few minutes. 

 
Here’s the background.  The Customs Service is charged not only with preventing marijuana from entering or leaving the U.S. but also with tracking where the stuff is grown or gathering information about growing locations. Carbon isotope analysis can be used as a powerful forensic tool to narrow down the growth locations of marijuana to specific regions and to determine whether it was grown indoors or outdoors. (Here is an article that discusses how this works). Indoor growth is common in many areas, including in both warm and cool climates. Indoor marijuana smuggled into the U.S. is primarily attributed to Canadian sources. Outdoor-cultivated crops are mainly sourced from Mexico.
 
Tracking the isotopes could provide useful information about the law enforcement and policing efforts in those respective countries. Ultimately, CBP scientists hope to use the CM-CRDS to understand the trafficking patterns related to the supply of marijuana to different markets across the United States. Stable isotopes in marijuana are molecular-level signatures created by photosynthesis and carbon uptake by plants. Stable isotope ratios of plants are extremely difficult to alter. So these isotopes should be a remarkably reliable and nearly immutable natural tracking mechanism - Nature’s Bar Code, if you will (we like to say that around Picarro).
 
The CM-CRDS system could also be used to detect adulterated products getting into the U.S. markets such as packed honey adulterated with high fructose corn syrup (HFCS) using stable carbon isotope analysis to elucidate the botanical origin of analyzed samples. In general, agriculture products and their derivatives fall under two main plant categories, the C3 and C4 plants. Corn and sugar cane are both C4 plants with a very distinctive carbon isotope signature while the rest of the crops fall either under the C3 plants category or under a hybrid of both C3 and C4 metabolism. Authentic honey has a typical carbon isotopic signature of C3 plants which is well discerned from the C4 crops.

Synthetic versus natural products can also be differentiated using stable carbon isotope analysis such as vanilla. False claims regarding the authenticity of food products take place for economic purposes for fraudsters to benefit from tax breaks or to adulterate with cheaper products for economic gain. These types of analyses have been around for decades but only now with the CRDS analyzers (which is far easier to use and field deployable compared to lab-bound and complicated Mass Spectrometers) can agencies and corporations use stable isotope techniques almost anywhere they want and without the need of Ph.D. scientists to operate them. So analyzing the isotopes of marijuana is really only one possibility of using Nature's Bar Codes for all manner of forensic research.