the DZM was for the gas flow, yes? I’ll stick with nice safe hydrogen… he said as he set out on the Hindenburg bound for America.
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Derivitizations are useful for a lot of different analyses…I did sugars by GC (alfalfa sugars!?) for part of my PhD work and it worked great. There are lots of different approaches, depending on your targets and analytical setup (e.g.: there are derivatives for TLC and HPLC that put on groups that confer fluorescence. Methylations with diazomethane [explosive!?] are often used for fatty acids). What we’re discussing here is the creation of silyl ethers, built off hydroxyl groups. My sugar work way-back-when used HMDS (hexamethyldisilazane), and that reagent was effective for my problem. BUT, I’ve had mixed success forming cannabinoid derivatives. Mostly around reproducibility. Some thoughts:
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I’ve used BSFTA+ 1% TMCS (N,O-bis(trimethylsilyl) trifluoroacetamide, with 1% trimethylchlorosilane as a catalyst); this is the most commonly reported silylating reagent in the cannabis literature. The TMCS might be omitted if pyridine (proton scavenger solvent) is added, but I haven’t tried this yet.
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I believe (haven’t proved!) that your sample has to be quite dry before adding the derivatizing reagents. Blowing N2 over the sample, and gentle heating (e.g.: <40 C) works well.
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Remember that ALL compounds in your sample that have hydroxyl groups will be dervatized along with THCA/CBDA, etc., which means their retention times will shift, and if using a mass spec, the spectra will be different, from the added groups.
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Silating reagents (BSFTA, MSTFA, HMDS, all of them) are extremely reactive (read: corrosive! Personal experience…) to organic compounds, which include your skin, eyes, and lungs!! Nitrile gloves, wrap-around safety glasses, good ventilation are all mandatory!
I’m planning another campaign with this approach with my HP GC/MS (>20 yrs old): 6890 GC w/5972 MS + autosampler. Put together from eBay and donations, so it is possible to get there on the cheap. Finding the right version of MSD Chemstation software to drive the thing can be challenging.
Keep in mind that with this approach quite a number of targets can be measured by GC, including sugars, and with the right reagents, fatty acids and other compounds we’re interested in. Does take homework to get sample preparation, retention times, etc. worked out, but it allows broader coverage with your base instrument.
Here’s an Aldrich tech note on derivitization that’s pretty comprehensive:
4537.pdf (176.7 KB)
This also might help:
5.pdf (463.1 KB)
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There is (almost) no way to edit the poll after the first vote has been cast.
Possible course of action is to hold multiple rounds of polls, or a pre-poll asking for input on options. Limit each poll using the ‘automatically close poll’ option to ~1 week. IMO If there was any kind of serious vote or election we would use a more sophisticated system.
Interesting note: The co-creator of this forum software (discourse) says about polls “I too thought polls would be more useful, but I find polls to be of very limited use on a discussion site. You want explanations and discussions and explorations… not context-free snap judgments that hew to a very narrow set of inflexible, predefined options. (For example, I find that the best “option” is often one that I hadn’t even thought of…)”
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Hey guys, I know its a tangent but for a different kind of testing. Good for onsite genetic testing/dna amplification
PCR is a very useful technique. Not the first I’d bring in-house, but certainly on the list.
How exactly are you applying it to learn more about your cannabis?
are you using marker assisted selection? DNA based sexing?
Edit: as cute as that kit is, I wouldn’t bother with it even for DNA based sexing. I’d get a real machine used. A PTC-100 can be had for less than $400. I do like the LED based transilluminator. definitely beats EthBr & UV.
…and of course the low price leader: TLC, where $160 will get you up and running
I have no experience with this vendor. I have run TLC for state mandated testing in OR. Accuracy depends on the operator to a much larger degree than any of the other methods listed here imo. It can be very useful. I don’t currently have it in house.
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So I have the GC and just waiting on columns And standards. Does anyone know if you can install multiple columns? Otherwise every time I want to run terpenes I have to switch and recalibrate. That would be a pita.
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Yea we use for early sexing. To be 100% honest we grabbed it as a way to practice on site sexin. I wasn’t comfortable committing to a new 96well qpcr machine. It wasn’t till coming here I realized you could buy used lab equiptment. Grabbing the 96 well for that price would of been a much better choice. normally we run 12 test batches so having to run the minipcr twice is a time killer.
Also for those interested, https://www.medicinalgenomics.com/
Its more expensive per sex test than say mailing it in but once we expand to other tests (thc/cbd alleles) the cost per plant test comes down considerably.
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We have an SRI Model 420. It is a really cool idea… Built in hydrogen generator so you don’t have to pack around a cylinder of Hydrogen if you want to take it out to multiple facilities and do onsite testing, “Internal Standard” (Methyl Stearate) so you don’t have to spend money on expensive standards… etc. I found after LOTS of trial and error and many phone calls to SRI that I was unable to produce consistent test results with it though. I would see variations as big as 10% from test to test on the same sample. After many frustrated days spent trying to dial it in, I finally gave up and opted to just purchase R&D tests from our lab at $75 a pop. I have nothing against SRI and it could definitely be a problem with operator error… Just thought I’d share my experience.
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I have found all of the technicians I’ve trained on my SRI have started out fairly inconsistent. 10% error seems about right. if I was doing 3rd party testing I’d actually need to provide OR with each of their stats.
unless I use magnification on the syringe, there are definitely small bubbles that are contributing to this error rate.
The state certified labs here in OR are allowed a 20% margin between replicates before I’m allowed to call bullshit, so 10% isin’t as bad as it sounds.
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It makes it hard to know who is right. Your GC or the lab.
This GC has the built in air compressor and I got a third party H2 generator. Right now I am the only person who will be using it so any deviation is on me. Not to worried, ball park is good. \
When you say 10% deviation your talking 99% down to 90%? That’s a fairly significant swing. I will probably run tests x3 or 4 and average.
Only like 3k into the whole thing so its gonna be worth what I paid 
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the only way to do it right is to do it yourself…which means if you know your own error rate, having repeatedly injected the same sample 10x and asked excel how good you are, then you can know who is right. or at least redo your injection, and then know.
so long as you don’t remove the column from the detector, or change the hydrogen flow, the FID response is incredibly stable. I’ve loaded 4 year old calibration files and gotten reasonable numbers. I’ve currently got everything calibrated with CBD isolate. which came to me labelled 98% pure.
I haven’t done a thorough comparison to our current 3rd party lab, but was dialled in nicely to our previous lab.
yes. if you examine the syringe you’re injecting with, I think you’ll understand why injection is probably the biggest source of variation.
if you’re looking a flowers, the variance between flowers on the same plant is a huge eye opener.
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oh yes, flower is always variable. I am a bit bummed about the column issue. I also bought terp standards and terp columns. I am not sure I will use them now…
What about Big Sur Scientific or GemmaCert analysers? Has anyone tried these? Opinions?
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The GemmaCert is selling for less than $3k, assuming it’s not vaporware. also IR based. currently lists “total” THC & “total” CBD, which I assume means no resolution of the acidic from decarbed. Which seems off, given that everyone else doing IR is resolving those. they also look to have a $ per test scheme they’re planning to implement. suggesting the actual analytics might be web-based.
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The only way to run two columns is with a separate injection port and detector. Agilent makes dual column capable GC’s.
You can add those things to many SRI GC’s. Probably not the 420
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I have an 8610c. Looks like I could mount a second column with a drill but need a second fid. I think I have another option though.
The guys at SRI rock. So much support for a used unit and a few parts purchased.
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Just got off the phone with Big Sur Scientific.
Impressed enough that I asked them come on here and tell us about their instrument rather than have me paraphrase their spiel.
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I met them in San Jose at the T&T conference a few months back. The bit I got to spend with them was interesting. I’m so far in the preliminary stages of my project that the details of the in house analyzer are not priority.
Looking forward to hearing an insider view.