Chromatography Forum

so everything so far is going smoothly in getting all the things in order to sample and test mmj here in California. But am at least a month or two away from having everything I need to actually start testing. I imagine I will have a lot of questions once I am ready to actually start running samples but right now that is a ways off. I am going to be using an FID on an HP5890 and reading using an old 3396b integrator. I am really excited about the whole endevor and cant wait to get to work. I have talked with a lab in Colorado who does this and also read a number of procedures online and with anything there are always slight variations in the procedure and one variation that I feel is important is how much solvent to use. I read the procedure in the SRI website and the tell you to take 100mg of dried mmj sample and put it in a 40 ml vial then fill the vial with a solvent like methanol, but never specifies how much solvent to use. I am guessing 40ml since it just says fill up the vial, but isnt the amount of solvent used important to the dilution in your reading? The lab in colorado said they used "100ml methanol to 1/10 gram" of mmj (isnt that the same as 100mg?) and compared them against the exact same restek calibration standards (external) as the SRI procedure but isnt that more than twice as diluted as the SRI instuctoins. So I guess what I am asking is how do you take into accound the various dilutions of samples in solvents. I'm guessing this has something to do with calibrating from the integrator.

Dilutions are very improtant, if you are too concentrated you can overload the detector if you are too dilute you won't see anything.

If you have already talked to a lab that is using 1/10 gram per 100 mL... I would stick to that concentration as a starting point.

Personally, I would never say 1/10 gram per 100 mL, I would just say 1 mg/mL, so if you want to make a 40 mL test solution you should use 40 mL x 1 mg/mL = 40 mg of sample.

so if the peaks are visible over a range of concentrations, does the concentration matter for figuring out the percent in the end? I will go with her reccomendations of 1mg/ml but want to understand the process a little better rather than just follow her procedure.

Are you reporting as percentage of the plant matter or percentage of active compounds?

well, Ideally I think I am trying to figure out the percent THC, CBN and CBD and I guess that is relative to total plant matter. I kinda dont like explaining what I'm trying to accomplish because I feel like everyone thinks I'm just some pothead or something, but what I'm ultimately trying to do is trying to breed and develop a strain that produces over 27% thc. It is in the preliminary phases, and everything is legal and medical. Many medical seed companies online rate thier potency and it often ranges from 10%-24% occasionally higher (Y griega by medical seeds is supposed to be 27%, along with Satori by Mandala seeds and Tut by Pyramid seeds was once rated 33% in a competition in spain, but is advertised at 22%) The companies never say exactly what they are measuring so we are just left to assume that means % out of total bud. I should probably ask the lab in colorado just to make sure but dont want to pester them too much.

edit: did some research and it is supposively %weight thc to %weight dried cannabis

It appears you're right, it's percent of total matter. In this case, your dilutions are quite important; a general analytical chemistry text will be your friend to help with understanding calculations.

I lol'd at the first line of this abstract: http://onlinelibrary.wiley.com/doi/10.1 ... 3FA.d03t01
"Cannabis sativa L. contains more than 420 different constituents."

You know I find it really funny too, restek even says "At Restek, we’re into medical marijuana, from an analytical standpoint, as cannabis is one of the most complex (and controversial) natural products. That complexity can make it very challenging to analyze, especially as the suite of analytes expands beyond the usual cannabinoids (e.g. delta-9-THC, cannabidiol, cannabinol) to include other cannabinoids (e.g. cannabigerol, cannabichromene, delta-8-THC, cannabivarin, etc.) and terpenes, sesquiterpenes, oxygenated terpenes, and pesticides." Anyways screw smoking it this stuff is interesting as hell, I am completely fascinated with analyzing it at this point.