Regioisomeric differentiation of the alkyl-substituted synthetic cannabinoids JWH-122 and JWH-210 by GC-EI-MS/MS

Synthetic cannabinoids (SCs) are known to have structural or positional isomers. While regulations on synthetic drugs like synthetic cathinones and SCs have been placed worldwide for the ever-growing variety of new designer drugs, laws may not necessarily be applicable to their isomers. Toxicological differences may also exist among isomers for which most new designer drugs are still uninvestigated; thus, isomer differentiation becomes of forensic importance. The aim of this study was to differentiate the regioisomers of alkyl-substituted naphthoylindole-type SCs JWH-122 and JWH-210. Reference standards of the two drugs and their regioisomers were analyzed by gas chromatography–electron ionization-mass spectrometry (GC–EI-MS) first in full scan mode. Isomers that produced identical EI spectra were further analyzed by GC-tandem mass spectrometry (MS/MS) by selecting appropriate precursor ions. For JWH-210, comparison of the product ion spectra and the relative ion intensity ratios obtained from precursor ions at m/z 312 and 183 enabled differentiation between all seven regioisomers. Complete isomeric differentiation by MS/MS analysis was not attainable for JWH-122; however, combining chromatographic results with MS/MS analysis results enabled differentiation for all isomers. Two basic fragmentation pathways were speculated for both SCs; for JWH-210, fragmentation pathway tendencies differed among the isomers, resulting in their distinguishability. Our results demonstrated that the difference between the methyl (JWH-122) and ethyl (JWH-210) group substituents contributed to fragmentation pathway tendency differences and further distinguishability between the regioisomers. Functional group differences, especially their stereochemistries, were indicated to be critical factors in positional isomer differentiation by GC-MS/MS.