Limit of quantitation (LOQ)

Every analytical method has a floor. Below a certain concentration the instrument still sees a signal but cannot put a trustworthy number on it. The limit of quantitation is the lowest level at which the laboratory has validated that its value is accurate and repeatable; accreditation to ISO/IEC 17025 requires that it be validated rather than assumed (ISO). It sits above the limit of detection, the level at which presence can be seen at all. Anything above the LOQ gets a number; anything below it gets a less-than symbol or a not-detected result.

The LOQ defines what a not-detected result is worth. On the PharmLabs kratom reports linked from this store, mitragynine's LOQ is 0.054 ppm and 7-hydroxymitragynine is reported as not detected at an LOQ of 0.025 ppm (NarcoBrands COAs), which is 0.000025 mg per gram against the pending federal line of 1 mg per gram (91 FR 65370). A laboratory whose method could not see below 1 mg per gram could never show a product under that line, which is why this store prints the LOQ beside every not-detected result.

The same logic governs hemp. A lab with an LOQ of 0.1 percent for delta-9 THC will report ND for a product that holds 0.09 percent, which in a 30 mL tincture can be many milligrams. The amended federal hemp definition caps finished products at 0.4 mg total THC per innermost container (7 U.S.C. 1639o), so proving compliance needs an LOQ low enough that ND times container size stays under 0.4 mg. USDA requires labs to report measurement of uncertainty alongside THC results, a related statement of how precise a number is (7 CFR 990.1).