Thanks for your comment! From your post, it sounds like you're actually asking two questions: do I have any suggestions for your method of potency testing for leaves, oils, etc. and should you consider using QuEChERS as the extraction method of choice for all your analyses. I have two answers for you: yes, and no. I hope that helps...just kidding.
With regards to your potency testing for leaves and such, I think your current extraction method is pretty much okay. It seems like that’s what a lot of people are doing, and it works pretty well. The reason why it works so well is that leaves contain massive amounts of THC and not a whole lot of other stuff. Yes, there are definitely pigments and sugars and other plant compounds (I’m a chemist, not a botanist!), in your leaves, but you can get away with a small sample size because of the level of THC in the sample, thus ‘diluting out’ your interferences. My only suggestion for your method is to use a larger sample and grind the sample prior to extraction. This ensures that you get a homogeneous, representative sample that can be easily extracted. It’s easier to get compounds out of small pieces of things rather than big chunks, right? That being said, feel free to take or leave my suggestions.
Moving on to the edibles testing, the reason why this is so much more problematic is that the THC content in products like brownies should be much lower than in leaves and oils because of all the extra stuff there in the edible product – it has to taste good, right? Since I’m a chemist who was pretty lame in college, I don’t know how potent these edibles are, but I’m pretty sure they’re nowhere close to the realm of leaves or oils. Feel free to correct me if I’m wrong! So now, instead of extracting a sample that has massive amounts of THC and not much else, you’re trying to extract something with a small amount of THC and a lot of fat, flour, sugar, and cocoa. This is where QuEChERS really shines. By using QuEChERS, you can quickly and easily extract out your THC and clean up a lot of the extra stuff in the sample that will interfere with your analysis and crud up your instrument. Your description of the QuEChERS process was actually pretty good, basically, you take some brownie or other edible, add water and acetonitrile, add salts, shake it up, and centrifuge it.
At this point you’ll have an acetonitrile extract that contains your THC, but it also contains a lot of the other food ingredients as well. I wouldn’t recommend injecting this on your instrument unless you like cleaning burnt food out of your injection port. Fortunately, it’s relatively easy to clean up a lot of the food interferences. To clean up the sample, you just take a portion of the acetonitrile extract and shake it up again with some other products that are designed to remove fats, sugars, and pigments. Centrifuge that down, and you’ll have a much cleaner sample ready for injection. The great thing about these cleanups is that they can be tailored to different edibles. If you have a hard candy, then you can just use something to remove sugars and pigments because you don’t have to worry about fats.
I do have a couple of draft methods for edibles, but I don’t want to post them here for public consumption, because in all honesty, I’m not sure if they work. Unfortunately, marijuana is still completely illegal in Pennsylvania, so I have no way to test authentic samples. That being said, feel free to have Allan give me a call and I’ll tell him everything he wants to know and try not to bore him to death in the process.
Thanks again for posting! By the way, even with a chemistry degree, one can get themselves into trouble developing analytical techniques. I try to consider the pain and suffering of method development a character-building exercise.