Higher Instrument Peaks Did Not Change the Calculated Cannabinoid Concentrations
During extract testing, absolute peak areas increased while calculated cannabinoid levels remained unchanged. The distinction illustrates why a larger instrument signal is not automatically evidence of more drug in the original specimen.
The study reported two different observations
The automated assay developers observed absolute peak areas increasing by as much as a factor of three in the tertiary extract over the tested period. They considered evaporation of the derivatization reagent a likely explanation. However, concentrations derived from the ratio of target-compound signal to internal-standard signal remained unchanged.
The ratio was the quantitative basis
An internal standard can track changes shared by the analyte and reference signal. If both signals rise together, their ratio can remain stable. That does not mean internal standards correct every possible failure: unequal effects on target and standard still require investigation. It means raw peak size alone is an incomplete account of how this method produced a concentration.
Use the right comparison
When a chromatogram changes on reinjection, review target and internal-standard responses, calibration and calculated concentrations together. The authors’ likely evaporation explanation should not be asserted as proven for another batch. Their result concerns prepared laboratory extracts under specified conditions, not cannabinoid accumulation in a living person or a change in functional impairment.
Related analysis: the automated cannabinoid assay.
Research cited
Frei and colleagues (2022). Quantitative determination of five cannabinoids in blood and urine by gas chromatography tandem mass spectrometry applying automated on-line solid phase extraction. DOI: 10.1002/dta.3241.
