A common question we get is, "Can tCheck measure THC and CBD separately?" The short answer is unfortunately, no. The next question is, "why not?"
When we created tCheck, we based the underlying technology on a machine called an HPLC which is the gold standard today for testing cannabinoids. HPLC stands for high pressure (performance) liquid chromatography. An HPLC machine consists of lots of parts but two are particularly important: the column and the detector. The column in an HPLC is a tube that is packed full of some sort of coated granules. The coating is specially designed to be somewhat sticky. This stickiness is important. The detector sits at the end of the tube or column and detects when stuff passes all the way through the tube.
The main concept of the HPLC is that compounds, such as THC have a certain stickiness in the column while other compounds such as CBD have a different stickiness. For example, CBD is much less sticky than THC.
There are a few key things to keep in mind about an HPLC:
| Requirement | Details |
|---|---|
| Liquid Samples Only | Solid samples like cookies must be infused or extracted into a liquid solvent before testing |
| Beer-Lambert Principle | Has maximum limitation of measurement accuracy (linearity). Samples may need dilution to measurable range |
These limitations are important and are covered in a separate blog article. Back to running the HPLC. The first thing that the operator must do to prepare a sample for measurement is to turn it into a liquid. Usually this means infusing or soaking the sample in a solvent such as acetonitrile or methanol. Then this liquified sample is filtered and injected into the HPLC column. This column with the granules is called the "stationary phase". Once this happens, the HPLC starts doing its thing. Using a series of pumps, the HPLC then flows another solvent into the tube and this is where the stickiness of the cannabinoids matter. This second solvent is commonly known as the "mobile phase". Some cannabinoids are super sticky so are able to hang on to the granules in the column longer. Other compounds are not as sticky so it lets go sooner.
I grew up in the 70's and 80's so playgrounds had a merry-go-round. One of our favorite games was to all get onto the merry-go-round then start spinning it faster and faster. The smaller kids would get flung off first because their grip strength wasn't as strong while the older kids were able to stay on longer. Eventually, almost everybody got flung off.
The HPLC is just like that. When we first inject the sample into the column, it is like getting all of the kids onto the merry-go-round. We loaded the column. Then the HPLC machine starts pumping an increasing amount of solvent through the column (or, in some cases, a changing blend of different solvents). This is like spinning the merry-go-round faster and faster.
The detector at the bottom of the HPLC column sees when the compounds are flung off of the column and times when that happens. CBDa has the least amount of stickiness so falls off first at about 3 minutes and 20 seconds (3:20). CBD hangs on longer and finally lets go at about 4:10. Delta-9 THC hangs on until 6:30, then finally THCa falls off at 7:15.
| Cannabinoid | Retention Time | Stickiness Level |
|---|---|---|
| CBDa | 3:20 | Least sticky (falls off first) |
| CBD | 4:10 | Low-medium stickiness |
| Delta-9 THC | 6:30 | High stickiness |
| THCa | 7:15 | Highest stickiness (falls off last) |
The detector itself is just a UV-Vis spectrometer (see blog on how a UV-Vis spectrometer works). The more stuff there is, the darker. tCheck is simply the detector part of an HPLC. In the graph, this is represented by height of the peak.
So, combining the time at which the compound is released off the column and the how much is flung off the column, an HPLC measures and calculates the amount of each cannabinoid there is in the sample.
Going back to our merry-go-round example, we'll simplify by imagining that there are only 3 types of kids. Toddlers, tweens, and teens. All of the toddlers get flung off first and by measuring the combined weight of the toddlers, we can calculate how many there were. Likewise for the tweens, then finally for the teens.
An HPLC typically runs about $35,000~50,000 plus you'll need a bunch of very expensive chemicals to run it and calibrate it. Not to mention a trained technician to operate and maintain it. Obviously, this is beyond the reach of consumers or even most smaller growers and manufacturers.
Explore affordable home cannabis potency testing with tCheck →
tCheck tries to simplify the problem by assuming that most consumers know whether their material is THC or CBD dominant and whether they've properly decarboxylated (activated) it. In our merry-go-round analogy, we know that most or all of the kids on the merry-go-round are tweens. Then, all that needs to happen is to measure the total weight of the kids.
Want to understand more about cannabis potency testing methods? Or learn how to test cannabis edibles at home?
