How is the concentration of THC in marijuana measured?
Many drugs of abuse are analyzed using chromatography. Tetrahydrocannibinol (THC) is usually determined using gas chromatography (to separate the THC from the hundreds of other compounds present) followed by mass spectroscopy (to verify that the component separated was indeed THC). Here’s a sketchy outline of the procedure: • Extraction. The sample is extracted into an organic solvent like pet ether or methanol. • Evaporation. Some of the solvent is evaporated off to concentrate the sample. • Gas Chromatography (GC). The sample is placed into a syringe an injected into a port on the GC. The port is hot enough to vaporize the sample. The vapor passes into a long tube (the “column”) lined with a silicone polymer (something like Silly Putty), and an inert gas (like helium) sweeps the sample through the tube. As the sample moves along, the silicone polymer temporarily retains components in the passing stream. Some components are retained more than others; each has a characteristic “retenti
