Methanol Helped Address Cannabinoid Loss to Preparation Materials
The urine assay developers added methanol before cleanup to reduce cannabinoid loss to preparation materials. That procedural choice addressed adsorption during measurement rather than cannabinoid elimination inside a person.
Lipophilic compounds can interact with laboratory surfaces
Wei and colleagues identified tips and ninety-six-well plates as potential sources of analyte loss during sample preparation. Their method added 0.3 mL methanol to all samples before solid-phase extraction. They also discussed adsorption to instrument surfaces as a distinct source of potential carryover.
Loss and carryover are different consequences
Material left behind during preparation can reduce the amount reaching analysis. Material retained in an analytical pathway can also affect a later specimen. These possibilities require appropriate recovery and carryover experiments; one cannot infer the direction or size of an error in a particular case solely from the compounds’ lipophilicity.
The preparation recipe belongs in interpretation
A laboratory that changes solvents, containers or disposable materials needs supporting performance data for the revised workflow. The published methanol step is not a universal correction factor or permission to alter a collected forensic specimen outside an authorized procedure. The study validated a human-urine analytical method, not a method for reconstructing the person’s absorbed dose or functional impairment from adsorption losses.
Related analysis: the urine assay’s two analytical ranges.
Research cited
Wei, Wang and Blount (2015). Analysis of Cannabinoids and Their Metabolites in Human Urine. DOI: 10.1021/acs.analchem.5b02603.
