Limit of detection (LOD)

The limit of detection is where a method first sees a compound. A lab runs blank samples, measures the noise, and sets the LOD at the signal level that can be distinguished from that noise with confidence. Below it, the method cannot say whether the compound is there at all; such a result is "not detected." Between the LOD and the higher limit of quantitation, the laboratory can say the compound is there but not reliably how much, and the result is reported as "detected, below LOQ" or "less than LOQ."

The kratom reports linked from this store print both floors for each analyte: mitragynine LOD 0.018 ppm and LOQ 0.054 ppm, speciociliatine LOD 0.004 ppm and LOQ 0.011 ppm (NarcoBrands COAs). Both are properties of the validated method, which an ISO/IEC 17025 accreditation audit covers (ISO). The site prints the LOQ beside a not-detected result because the LOQ is the number regulators compare against their caps.

The distinction matters when a hemp label says THC-free or non-detect. Non-detect strictly means below the LOD. Some labs and brands use ND to mean below LOQ instead. Either way, the number that defines it must be on the report, because a non-detect at a high LOD proves less than a quantified value at a low one. USDA's hemp rules add a parallel requirement that labs report measurement of uncertainty with THC results (7 CFR 990.1).