The GC–MS method extracted parent THC first and then changed the remaining phase for THC-COOH recovery. Its performance belonged to a two-stage preparation, not a single universal extraction step.
The sequence was part of the assay
After internal-standard addition and basic preparation, the workflow used a hexane–ethyl-acetate mixture to recover the parent-drug fraction. The remaining aqueous phase was subsequently acidified and extracted again for the carboxy metabolite. The metabolite fraction then underwent derivatization before analysis.
The details matter because THC and THC-COOH have different chemical behavior. A reported recovery for the complete method does not demonstrate equivalent recovery if the second stage is omitted or rearranged.
A modification requires its own evidence
Replacing two stages with one, changing the phase conditions or testing another matrix can alter selectivity and recovery. The paper does not establish that every such alternative fails; it simply does not validate them by having validated the stated workflow.
Keep analytical and biological conclusions separate
The human postmortem case application showed practical use of the method, with important specimen-preparation qualifications. It was not a living-person dose or performance experiment. Successful separation and quantification cannot independently reconstruct antemortem impairment, last-use time or the role of cannabis in a death.
Related reading: limits of postmortem cannabinoid reporting.
Research cited
Álvarez-Freire and colleagues (2023). Simple Method for the Determination of THC and THC-COOH in Human Postmortem Blood Samples by Gas Chromatography—Mass Spectrometry. DOI: 10.3390/molecules28083586.
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