Understanding THC Potency Measurement
In the cannabis world, the active ingredient is Delta-9 tetrahydrocannabinol (Delta-9 THC). Measuring potency typically means determining how much THC is in the sample.
Chromatographic Separation of THC
Chromatographically, THC analysis is one of the easiest things to do. If you run any HPLC instrument with a reverse-phase C18 column, using 70% acetonitrile-water or 70% methanol-water, you will achieve a clear separation of cannabinoids.
For the most part, in natural cannabis, you will observe one dominant peak at around 230 nanometers (low UV range). This giant peak represents Delta-9 THC, as there is little else that absorbs at this wavelength.
Sample Preparation for THC Testing
To measure potency accurately, here are the the key steps to sample preparation:
- Weigh the sample – Start with a precise weight (e.g., 1 gram).
- Extract the THC – Use 100 mL of methanol,
- Sonicate it for about an hour or overnight to accelerate extraction.
- Analyze the liquid extract – This will determine the THC concentration in the sample.
Want more tips about sample prep? Watch the webinar “Analyzing an Unknown – Start to Finish” with a free Axion Lite membership.
Differentiating THC from THCA
HPLC has the advantage of differentiating THC from THCA.
- THCA (Tetrahydrocannabinolic acid) – The non-psychoactive precursor to THC, naturally present in cannabis.
- THC (Delta-9 THC) – The psychoactive compound formed when THCA is heated (e.g., via smoking or decarboxylation).
A raw cannabis plant will have high THCA and low THC, whereas a distillate will contain mostly THC with little or no THCA. If you need to measure the difference between THC and THCA, use HPLC.
GC vs. HPLC: Which One to Use?
- HPLC (High-Performance Liquid Chromatography)
- Best for differentiating THC from THCA.
- Requires no heating, so THCA remains in its original form.
- Ideal for raw plant material testing.
- GC (Gas Chromatography)
- Best for measuring total THC potency.
- Heat converts THCA to THC, meaning you get a measurement of total available THC.
- More suitable for distillates, extracts, or potency screening.
Choosing an HPLC for THC Analysis
If you are considering purchasing an HPLC for THC testing, here are some key recommendations:
- Even the simplest HPLC system will work for basic THC testing.
- If you plan to run tests daily, invest in a robust system with a warranty.
- Consider buying used equipment from Shimadzu or Agilent, both reputable brands in chromatography.
- A gradient HPLC system is ideal, but an isocratic system is technically sufficient for THC analysis.
- Use a UV detector:
- Diode Array Detector (DAD) is preferred.
- A Variable Wavelength Detector (VWD) also works well.
- Set the detection at 230 nanometers to capture all cannabinoids.
Conclusion
If you need to measure total THC potency, GC is the simplest approach. However, if you want to differentiate THC from THCA, HPLC is necessary. Both techniques have their advantages, so choosing the right one depends on whether you’re analyzing raw plant material or final distillates.
