Picograms Per Breath Pad Were Not Picograms Per Liter of Air
The breath assay reported recovered cannabinoid mass per collection pad. That unit should not be relabeled as concentration per liter of exhaled air without the necessary sampling-volume information.
The collection was time-based
Participants breathed normally through the collection arrangement for three minutes, inhaling through the nose and exhaling through the device. The polymeric filter pad was then sealed and processed. The assay’s THC quantification limit was 50 picograms per pad. This expresses recovered analyte mass for the collection system.
A volume concentration has another denominator
A three-minute collection does not, by itself, establish that every participant exhaled the same volume. Dividing by minutes instead of measured air volume produces a different quantity. Collection efficiency also matters to any attempted conversion from recovered pad mass to the amount originally present in breath.
Compare like measurements
When comparing devices or studies, retain units, duration, breathing instructions, recovery and any volume normalization. The paper does not supply a universal conversion from pad mass to blood THC or an impairment threshold. Its human controlled-smoking observations remain specific to the collection and analytical system, including actual collection timing and the possibility of nondetection after known exposure.
Related analysis: actual breath-collection timing.
Research cited
Himes and colleagues (2013). Cannabinoids in Exhaled Breath following Controlled Administration of Smoked Cannabis. DOI: 10.1373/clinchem.2013.207407.
