Delta-8-THC (D8-THC or (-)-Δ⁸–trans-THC) is a psychoactive substance that differs chemically from Delta-9-THC ( D9-THC or (-)-Δ⁹–trans-THC) only in the location of one double bond in the THC molecule. Delta-8-THC and Delta-9-THC have the same numbers of carbon, hydrogen, and oxygen atoms, the same molecular weight, the same stereochemistry, and nearly the same three-dimensional shape. Consequently, Delta-8-THC and Delta-9-THC are nearly identical cannabinoids that share many chemical, physical, and pharmacologic properties. 

Figure 2. Structures of Delta-8-THC and Delta-9-THC compared

The close chemical and physical properties of Delta-8-THC and Delta-9-THC make them a challenge to separate by high performance liquid chromatographic (HPLC) methods when reversed-phase separations are used. If the HPLC instrument is connected to a UV-visible light detector, Delta-8-THC and Delta-9-THC produce nearly identical absorption spectra so they cannot be differentiated based on differences in their UV spectra so the only way to identify them by HPLC methods with UV-visible detection is to separate them chromatographically. Modifications of mobile phases and use of more efficient chromatographic separations can produce baseline separation of Delta-8-THC from Delta-9-THC thereby allowing them to be differentiated based on differences in characteristic retention times.

Although Delta-8-THC can arise in plant materials from acid-catalyzed isomerization of Delta-9-THC, the rate of this reaction in plant material is very slow so the amount of Delta-8-THC in natural plant material is so low that it is usually undetectable. Therefore, plant material is not a useful commercial source of Delta-8-THC, so it must be obtained from other sources. The Delta-8-THC that has been commercially available for several years is made by the acid-catalyzed isomerization of cannabidiol (see Figure 3). Delta-8-THC that is made by this method typically contains variable amounts of Delta-9-THC plus numerous side products. Two of these side products are Delta-8-iso-THC and Delta-4(8)-iso-THC (see side products in Figure 3). 

Figure 3. Conversion of cannabidiol (CBD) to Delta-9-THC and Delta-8-THC as well as side-products Delta-8-iso-THC and Delta-4(8)-iso-THC

Although these side-products have names that suggest a close relationship to Delta-8-THC, their shapes differ substantially from Delta-8-THC, and they probably do not possess any of the psychoactivity of Delta-8-THC or Delta-9-THC. If they have other pharmacologic effects, they have not been reported.

The physicochemical properties of these side products are so similar to those of Delta-8-THC and Delta-9-THC that they are not separated from them by reversed-phase HPLC methods. Delta-4(8)-iso-THC is not adequately separated from Delta-9-THC and Delta-8-iso-THC is not adequately separated from Delta-8-THC when the HPLC method that is widely used to determine cannabinoids in plant materials is used. 

The chromatogram in Figure 4 was obtained from the analysis of a Delta-8-THC product that contains Delta-9-THC as well as these side-products that are not adequately resolved. Consequently, concentrations of Delta-9-THC may be overestimated in Delta-8-THC materials because the D4(8)-iso-THC is not resolved from the Delta-9-THC. Alternatively, the Delta-4(8)-iso-THC, which appears slightly later than Delta-9-THC, overlaps the peak for Delta-9-THC and masks it so that it is not reported.

Figure 4. HPLC reversed-phase separation of a Delta-8-THC sample that contains Delta-9-THC, Delta-4(8)-iso-THC, and Delta-8-iso-THC

KCA Labs recognized and addressed this analytical challenge several years ago and developed a GC-MS method that completely resolves Delta-4(8)-iso-THC, Delta-8-iso-THC, Delta-8-THC, and Delta-9-THC chromatographically so that each substance can be quantified in a mixture containing these four substances plus other cannabinoids. The consequence of our use of this alternative and superior methodology is that we accurately quantify Delta-9-THC in Delta-8-THC samples that have been analyzed by HPLC because the presence of Delta-4(8)-iso-THC in these samples has masked the presence of Delta-9-THC when analyzed by HPLC. Since the GC-MS method separates Delta-4(8)-iso-THC from Delta-9-THC (see Figure 5) and is highly sensitive, samples of Delta-8-THC containing Delta-9-THC near the regulatory threshold can be determined more accurately and a clear distinction can be made between samples that contain more Delta-9-THC than is permitted. Consequently, a Delta-8-THC sample that is reported to contain no detectable Delta-9-THC when analyzed by HPLC may be found to contain  Delta-9-THC above 0.3% Delta-9-THC when analyzed by GC-MS. 

Figure 5. GCMS chromatogram illustrating separation between Delta-4(8)-iso-THC, Delta-8-iso-THC, Delta-8-THC, and Delta-9-THC