CBN Served as the Internal Standard in a Postmortem THC Assay
The postmortem GC–MS method used cannabinol as an internal standard. CBN was a reference signal in this procedure, rather than a second reported measure of parent THC or a stable-isotope-labeled copy of it.
Identify the reference compound
Paknahad and colleagues described adding CBN internal standard during preparation of urine for THC-COOH analysis and an internal-standard solution during blood preparation. Their reagents section identified CBN as the internal standard. The method measured THC in postmortem blood and THC-COOH in hydrolyzed urine, with different preparation and calibration conditions.
A different cannabinoid is not chemically identical
Using a related compound as a reference does not make its extraction, derivatization and detector response identical to those of each target analyte. Conversely, the choice alone does not prove that quantification failed. The appropriate evidence is the validation showing how the target and reference behaved together under the actual method conditions.
What the study does not resolve automatically
The presence of CBN in the reagent list should not be described as independent confirmation of cannabis exposure in each case. Nor should its use be silently relabeled isotope dilution. Review calibration, selectivity and internal-standard behavior before drawing an analytical conclusion. This selected postmortem application did not establish a concentration that proves impairment before death or cannabis causation of death.
Related analysis: the postmortem assay’s reporting limits.
Research cited
Paknahad and colleagues (2024). Enhancement and validation of a quantitative GC–MS method for the detection of THC and THC–COOH in postmortem blood and urine samples. DOI: 10.1016/j.mex.2024.102962.
