I am looking for a method blank which I can use in the heavy metals, terpene, solvents, cannabinoid, pesticide, and microbial analyses I do in my analytical lab on cannabis samples. I have tried Oven drying hemp to remove the residual solvents and terpenes because these are more volatile compounds. It worked for the terpenes, they were all burned off, but it did not work for the residual solvents analysis due to the inherent solvents that plants produce or uptake in their natural life cycle.
For heavy metals the samples failed due to the fact that almost all plants will have some amount of heavy metals in them from the soil they are in. Small amounts of cannabinoids were also found in the hemp so it did not work for potency testing.
Does anyone have any ideas for a suitable plant material that is similar to cannabis that could possibly be used as an "analyte-free" matrix for method blank purposes? I have heard of other labs using vegetable or hemp oils but I feel the matrix is not similar enough to cannabis flower to use in this instance.
I bet you are not developing all these methods for a university research, but for commercial regulatory testing lab, isn't it?
Let's break down the different tests:
1- Heavy metals: It's hard to find a plant without metals at all. So, use cannabis flower to make two aliquots, one to be extracted directly and the other to be spiked by some metals standard and then extract it. Subtract the unspiked from the spiked to calculate recovery.
2- Terpenes: You are right about what you heard. Use oils such as cooking oils or skin lotions.
3- Solvents: Same as terpenes, just subtract the values measured in the unspiked aliquot from the spiked one to calculate recovery.
4- Cannabinoids: Use a hemp matrix. Hemp doesn't have high THC, maybe no THC at all. Disregard the other cannabinoids, no one cares for them, focus of THC only.
5- Pesticides: Usually the cannabis flower is free of detectable pesticides, so you can use it as blank.
6- Microbial: No idea actually.
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