Dual wavelength analysis for cannabinoids

[fredindose]

Another weird phenomena. Our oil report says delta9-THC is at 76%.. the next component is CBC at 2%. Overall it says cannabinoids comprise 80% of the oil.

Going to look at our vapor via Shimadzu's dual wavelength UV detector.. there's a nice large delta9 peak at 280 nm, but also another really high peak, almost half of the delta 9 size; 254 nm shows a lot of dirt but the same thing with the peaks; 220 nm shows the aberrant peak a little bit smaller.. my question is.. does analyzing at different wavelengths distort some cannabinoids? I read a paper that shows CBC has maximal absorption at 280, delta9 at 220 but it still doesn't mean there's something else there besides delta9 at that high of a concentration, something is being picked up.. what the heck is going on here?

[blackmetalchem]

You may be getting co-elution of terpenes. A lot of the vapors add terpenes for aroma and flavor. They typically do not give much signal at 220nm and that is why this wavelength is used.

http://blog.restek.com/?p=33071

[James_Ball]

Are you calibrating the individual cannabinoids or just using area% to calculate the % composition of the oil?

If using area% the different response factors of the analytes at a given wavelength will throw the % composition off. The response factors using GC/FID would be close enough to do area% with some accuracy, but for HPLC/UV I would think not.

[fredindose]

We used Delta 9 THC, and CBD standards from cerilliant, they both had a Max at 0.25 mg/ml on a five point cal curve. We noticed that there were nice, very consistent peaks at 2.46 min for CBD and 3.43 min for delta9, for both the standards and our test samples, but again rogue peaks at 4.0 or funny enough 4.19 min about 1/4 the size of the delta9, which didn't make any sense.

[fredindose]

You may be getting co-elution of terpenes. A lot of the vapors add terpenes for aroma and flavor. They typically do not give much signal at 220nm and that is why this wavelength is used.

http://blog.restek.com/?p=33071

I read terpenes do not reflect or absorb UV light, if they are co-eluting how can they be causing any interference??

[blackmetalchem]

Really it depends on the terpene structure, but if you are getting rogue peaks and they are consistent and only in the sample not the standards then it is something to consider. If it is showing up in the standard as well then there may be some contamination issue. I only mention terpenes because I know they are added to vapes and unless you ask you may not be sure what they added unless you try another technique to characterize them.

[BostonFSE]

Is your diluent ethanol? Consider its UV cutoff when determining what wavelengths to choose. Each compound will have a chromophore for a specific wavelength so yes the area intensity differs with wavelength
Co-elution can be resolved by manipulating the gradient percentages, TCC temperature, column chemistry etc

Are you using a C18 with water w/0.1% formic acid as Mobile phase A? And ACN with 0.1% formic acid as mobile phase B?

If you have a DAD (diode array detector) you can look at the spectrum of those unknown peaks and try to deduce their identity. Its about the only way without a MS.
You can also "spike" a sample with another compound, Overlay, then if the peak grows in area, then you know the identity