HPLC pumps a liquid (the mobile phase) carrying the dissolved sample through a column packed with fine particles. Compounds interact with the packing differently and leave the column at different times. A detector, usually UV or diode-array (DAD), measures each compound as it exits, and comparison with reference standards turns peak size into concentration.
In practice
HPLC runs at or near room temperature, so THCA and THC, CBDA and CBD appear as separate peaks. That's why it's the default potency method for flower and concentrates. A typical cannabis method resolves around 10-17 cannabinoids. Its weaknesses: compounds without a reference standard, or that co-elute (come out together), can be misidentified or missed, and results still depend on sample prep and calibration. UHPLC is a faster, higher-pressure variant.
Don't confuse with
- GC: heats the sample and decarboxylates acids unless derivatised; used for terpenes and residual solvents.
- LC-MS: liquid chromatography coupled to mass spectrometry; more specific, used for pesticides and mycotoxins.
- HPLC grade: a purity grade for solvents, not a test.
THCA (tetrahydrocannabinolic acid) is the acid cannabinoid that drug-type cannabis makes in its trichomes; heat or time decarboxylates it into THC, losing about 12% of its mass.THC (Δ9-tetrahydrocannabinol) is the neutral, decarboxylated cannabinoid mainly responsible for cannabis's reported intoxicating effects; the living plant makes it almost entirely as THCA.CBD (cannabidiol) is a non-intoxicating neutral cannabinoid formed when CBDA decarboxylates; hemp-type and CBD-dominant cannabis make it mainly as CBDA in their trichomes.A cannabinoid is any compound that binds the body's cannabinoid receptors or shares the typical cannabis terpenophenolic structure; the plant-made ones are phytocannabinoids such as THCA and CBDA.Homogenisation is grinding and mixing a sample so every portion the lab tests represents the whole; together with representative sampling it often matters more than the instrument.Terpenes are volatile hydrocarbon compounds built from five-carbon isoprene units; in cannabis they are made in the trichome heads and are a major part of aroma and flavour.A residual solvents test measures leftover solvents such as butane, propane, ethanol or hexane in an extract, usually by headspace GC, against safety limits.Mycotoxins are toxic compounds made by certain moulds, such as aflatoxins and ochratoxin A from Aspergillus and Penicillium species; cannabis labs test for them at parts-per-billion levels.Potency testing is laboratory measurement of a sample's cannabinoid content, normally by HPLC, reported as % w/w or mg/g for each cannabinoid plus calculated totals.Gas chromatography (GC) separates volatile compounds in a heated gas stream; it is used for terpenes and residual solvents and decarboxylates acid cannabinoids in its hot inlet.LC-MS couples liquid chromatography with mass spectrometry, identifying compounds by mass as well as retention time; it is used for pesticides, mycotoxins and detailed cannabinoid profiling.Acid cannabinoids (THCA, CBDA, CBGA) are the carboxylated forms the plant makes; neutral cannabinoids (THC, CBD, CBG) form when heat or time removes the carboxyl group.The LOQ (limit of quantitation) is the lowest concentration a method can measure with acceptable accuracy and precision; below it a result is reported as <LOQ.
