Understanding Cannabis Testing Methods and Chemistry

Cannabis testing for potency is analyzed by using an industry standard method called High Performance Liquid Chromatography (HPLC) or Gas Chromatography (GC). The HPLC method is advantageous to the GC method because the GC produces high heat, making it unable to detect THCA properly. At high temperatures, above 115 degrees Celsius,  THCA begins to convert to d9-THC. Thus, HPLC is advantageous since it can be used at temperatures that don’t interfere with the THCA to d9-THC conversion pathway.

Decarboxylation is the chemical reaction that occurs when THCA is converted to d9-THC. At high temperatures, an increase in thermal energy occurs, which causes a carboxyl group (COO-) to be released as CO2 (figure). THCA decarboxylation to d9-THC results in a loss of a carbon and two oxygen atoms, which together weigh 44 atomic mass units (amu). Therefore, d9-THC should have 44 amu less than THCA. The molecular weight of THCA is 358 amu and d9-THC is 314 amu. The molecular weight ratio of d9-THC to THCA is 314/358, or 0.877. For example, for every milligram of decarboxylated THCA, 0.877 milligrams of d9-THC will be produced.

The total potential maximum of d9-THC that is available is calculated by compensating the end weight difference.

Molecular weight of d9-THC = 314 amu

Molecular weight of THCa = 358 amu

314/358 = 0.877

Total Potential Maximum d9-THC = (THCA amu) * (0.877) + (d9-THC amu)

A liquid chromatography (LC) instrument coupled to a mass spectrometer (LCMS) is another method for potency testing. This method is not widely used, but is more robust and reliable for accuracy – especially when analyzing very low concentrations of compounds. Cannabis flower or extracts contain cannabinoid concentrations ranging between 5-80% making the HPLC or GC method suitable for quantitation without losing significant sensitivity.

However, pesticide residues found on cannabis can be found at very low ranges thus making LCMS the standard method for pesticide testing because of its capability of detecting in the parts per billion (ppb) range.