Hi everyone. I’ve been reading that a lot of people on here prefer gas chromatography instead of hplc for potency tests. I was just kind of curious if anyone could speak on why?
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Really they do? I’d second I’d love to hear the argmunents. I’m rocking a sweet HPLC / DAD setup but I like some GC myself.
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I’d prefer HPLC with DAD over GC anyday
Gcs are way more finicky IMO and less accurate
Although they are easier to work on than an HPLC
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I’ve seen a lot of people asking about gc assays. I just don’t understand why for cannabinoids.
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The one good thing about tinkering with an hplc is that most manuals especially Agilent can be found online and are extremely useful
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i dont think anyone “Prefers” and FID-GC over an HPLC. Rather, an SRI GC can be had much cheaper and easier to learn how to use. also, you wont be packing up an HPLC into a shipping crate and traveling with it. An @srihugh1 GC can even be pieced together used for under a few grand and theyre easy to learn how to operate which makes them ideal for small shops to use and deploy. The idea that a small op can have in house analytics for cheap where an HPLC is not something a small medical caregiver like myself would ever be able to acquire or afford cant be ignored.
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I don’t think there is an overwhelming preference on this form.
As far as accuracy, you should have commensurate results between both gc and hplc. A lot of it comes down to sample prep, weighing, dilution, and system prep. The operator can have great influence on the results.
There are pros and cons to both.
GC is cheaper and less hazardous waste foot print because your mobile phase are inert gases. However GC is destructive testing in that your sample injection is exposed to heat so decarboxylation naturally occurs. So if you want to detect and quantify acidic cannabinoids You must do what is known as derivitization step.
EDIT: another pro for Gc is that they are more portable than the HPLCs
HPLC has a far more significant hazardous waste foot print. But you can measure acidic cannabinoid‘s directly because it’s non-destructive testing in that unlike GC your sample injection is not volatilized. HPLC’s tend to be more expensive but you can find older generations such as the Agilent 1100 for a pretty decent price. I’ve used several HPLC’s in the pharmaceutical industry and in the cannabis space and I’ve even had success using a Chinese HPLC from a company called CXTH base in Beijing China. If I recall correctly I think it was between three and four grand for binary pump, UV/vis detector, manual injector 4.6 mm x 250 mm C 18 column all included. Definitely better systems out there but it did what it was supposed to do. We use a free chromatography software for detection and integration called data Apex clarity software .
It was actually more intuitive to use than the waters empower software which is what they really like to use the pharmaceutical industry because it’s rocksolid audit supportHit me up if you have interest in the HPLC I really like working with those things and would be happy to share what I know
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GC vs HPLC for cannabis analysis:
- GC is less expensive to buy and much less expensive to operate. The solvents, lamp maintenance etc on a HPLC ends up costing 5-15 dollars per analysis. The GC costs about 15 cents. That’s a 100:1 difference. As noted above, there is no haz waste with GC. In fact the whole thing runs on distilled water. There is almost zero maintenance on the GC.
- The GC can test for terpenes, cannabinoids and residual solvents for no extra money. Can’t do that with the HPLC. The HPLC column lasts 300-500 samples. The GC column lasts forever.
- The HPLC measures the acidic forms of the cannabinoids ( THCA as well as d9THC ) whereas the GC converts the THCA to d9THC inherently in the measurement process unless a simple derivitization step ( extra 3 minutes work ) is performed prior to injection. This can be an advantage or a disadvantage. The advantage is that with GC you only need to calibrate on the neutral cannabinoids. With the HPLC you have to calibrate on twice as many molecules. This can get expensive and time consuming. In the end you multiply the THCA number by a factor to get the “total smokeable potency” which the GC delivers automatically. The calibration standard for the acid forms is unstable and 10 times the price so its easy to make HPLC errors when calibrating the acid forms.
The conversion factor between THCA and d9THC is in dispute. Its theorectically .877 but in reality is .68 so the HPLC answers are almost always higher than reality when measuring flower samples.
HPLC and GC agree perfectly when measuring decarbed concentrates. - The GC is portable. Just throw it in the truck or check it as airline baggage. The HPLC is delicate.
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As someone with experience using GC/MS as well as GC/FID and is currently using HPLC/VWD for in-house potency results I would say GC is easier to use and can be cheaper. Also, fragmentation due to the heat source can cause someone without inherent GC knowledge to misinterpret results. (Just reiterating my experiences with what I’ve read here)
The VWD is great - although I wish I would have gotten the diode array. I was trying to be simple and save the company I work for a little money. Not that the VWD is insufficient - but I would have more investigative capabilities when it comes to things like incorporating Vitamin e acetate standards into the calibration, etc. (Working on Agilent 1100 w/ chemstation software - all of this was purchased used).
Bottom line - proficient operators should be able to obtain trustworthy results from both instruments. I am happy to help anyone with HPLC questions pertaining to cannabinoids. My GC use was not with cannabinoids so I don’t want to offer any help there. I’m sure there are people here more qualified to do so.
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Did not see that till now, happy more are using in house analytics
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Looking at the links table (really useful when chasing rabbits around here) below the survey, you’ll notice the link above was the 50th pointing at that thread 
There really is soooo much information lying around here…
The signal to noise is not quite what it used to be, but I think we’re doing pretty well for a gang of drug addled thugs 
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Been there, done that. Little disappointed that I had to check the 420, was really hoping it fit in the overhead bin. 
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For potency as asked in the original question, I prefer an HPLC-DAD. But I have visions of grandeur, buying a SPME autosampler for the GCMS and cataloging aromatics. FID is too destructive, if I was using GC it would just be a GCMS. I also love my LCMS. You can never have too many instruments, lol. 
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Can the FID quantify vit e acetate, MCT oil, pg, vg?
Are any of those volatile compounds or thermally stable? The VItamin E-acetate has got 31 carbons - boiling point is high. I have also heard its susceptible to degradation before boiling point so maybe not suitable for analysis using gas chromatography - I am there could be some bias introduced due to that degradation before the proper compound in vapor state reaches the flame . Maybe I am wrong and @srihugh1 will come through. Samples need to be volatile and thermally stable - which makes terpenes suitable for GC
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The lack of hazardous liquid waste with GC is a real positive.
Proper waste disposal is expensive and improper disposal can result in some very serious charges if they don’t have anything else to hang on you.
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is this the setup?
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I would argue that with proper upkeep, you should be able to get more than 500 samples from an HPLC column. Albeit I am also using a guard column, its just a shorter version of the full column and I am well over 500 samples deep with no issues on this column
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