LC-MS separates compounds by liquid chromatography, as in HPLC, then ionises them and measures their mass-to-charge ratio. Tandem instruments (LC-MS/MS, triple quadrupole) fragment each ion and monitor specific fragments, which makes them highly selective and able to quantify trace contaminants in a complex plant matrix.
In practice
Testing labs mainly use LC-MS/MS for pesticide panels and mycotoxins, because it reaches parts-per-billion levels and separates target compounds from cannabis's crowded background. Research groups use high-resolution LC-MS for wide cannabinoid profiling: Berman et al. (2018), from Dr. Dedi Meiri's lab, used ESI-LC/MS to profile scores of phytocannabinoids, far beyond a routine panel. It's more expensive than HPLC-UV and needs careful calibration and matrix-matched standards.
Don't confuse with
- HPLC-UV: same separation, but a UV detector; cheaper, standard for potency.
- GC-MS: gas-phase separation with mass detection; used for volatiles and some pesticides.
- MS (alone): the detector, not the full method.
HPLC (high-performance liquid chromatography) separates compounds dissolved in a liquid under pressure; it is the standard cannabis potency method because it measures acid cannabinoids without heating them.A pesticide panel screens a cannabis sample for a defined list of pesticide residues, typically by LC-MS/MS and GC-MS/MS, reporting each against its action limit.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.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.A phytocannabinoid is a cannabinoid made by a plant, chiefly the terpenophenolic compounds cannabis builds in its glandular trichomes, such as THCA, CBDA and CBGA.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.The LOD (limit of detection) is the lowest amount of a compound a method can reliably tell apart from zero, but not necessarily measure accurately.
