title: Isomerization of delta-9-THC to delta-8-THC when tested as trifluoroacetyl-, pentafluoropropionyl-, or heptafluorobutyryl- derivatives.
abstract: For GC-MS analysis of delta-9-tetrahydrocannabinol (delta-9-THC), perfluoroacid anhydrides in combination with perfluoroalcohols are commonly used for derivatization. This reagent mixture is preferred because it allows simultaneous derivatization of delta-9-THC and its acid metabolite, 11-nor-delta-9-THC-9-carboxylic acid present in biological samples. When delta-9-THC was derivatized by trifluoroacetic anhydride/hexafluoroisopropanol (TFAA/HFIPOH) and analyzed by GC-MS using full scan mode (50-550 amu), two peaks (P1 and P2) with an identical molecular mass of 410 amu were observed. On the basis of the total ion chromatogram (TIC), P1 with a shorter retention time (RT) was the major peak (TIC 84%). To identify the peaks, delta-8-THC was also tested under the same conditions. The RT and spectra of the major peak (TIC 95%) were identical with that of P1 for delta-9-THC. A minor peak (5%) present also correlated well with the latter peak (P2) for the delta-9-THC derivative. The fragmentation pathway of P1 was primarily demethylation followed by retro Diels-Alder fragmentation (M - 15-68, base peak 100%) indicating P1 as a delta-8-THC-trifluoroacetyl compound. This indicated that delta-9-THC isomerized to delta-8-THC during derivatization with TFAA/HFIPOH. Similar results were also observed when delta-9-THC was derivatized with pentafluoropropionic anhydride/pentafluoropropanol or heptafluorobutyric anhydride/heptafluorobutanol. No isomerization was observed when chloroform was used in derivatization with TFAA. In this reaction, the peaks of delta-8-THC-TFA and delta-9-THC-TFA had retention times and mass spectra matching with P1 and P2, respectively. Because of isomerization, perfluoroacid anhydrides/perfluoroalcohols are not suitable derivatizing agents for analysis of delta-9-THC; whereas the TFAA in chloroform is suitable for the analysis.
authors.affiliation: Division of Forensic Toxicology, Office of the Armed Forces Medical Examiner, Armed Forces Institute of Pathology, Rockville, MD 20850, USA.
authors.forename: Justin M
authors.initials: JM
authors.lastname: Holler
authors.forename: Michael L
authors.initials: ML
authors.lastname: Smith
authors.forename: Shom N
authors.initials: SN
authors.lastname: Paul
authors.forename: Marilyn R
authors.initials: MR
authors.lastname: Past
authors.forename: Buddha D
authors.initials: BD
authors.lastname: Paul
mesh_terms: D013759:Dronabinol / Q000737:chemistry*; D017611:Fluorine Compounds / Q000737:chemistry*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D007536:Isomerism
chemical_list: D017611:Fluorine Compounds; D013759:Dronabinol