A color change can provide a quick analytical signal, but the reagent determines which compounds contribute to it. Houtzager and colleagues developed a paper-based device and tested two color reactions for different purposes. One reaction distinguished THC-rich from CBD-rich plant samples. The other estimated combined THC, CBD and cannabinol content in plant samples and oral fluid.
The combined signal answers how much of the targeted group the method estimated. A laboratory trying to report THC alone would need a measurement that distinguishes THC from the other cannabinoids. The study compared the paper device with gas chromatography–mass spectrometry in the samples examined.
When reviewing a result from a color test, identify the reagent, the sample type and the quantity it reports. A method evaluated for total cannabinoid content does not provide the individual concentrations that make up that total. The distinction matters when a report is used to support a claim about one specific compound.