Analytical differentiation of quinolinyl- and isoquinolinyl-substituted 1-(5-fluoropentyl)-1H-indole-3-carboxylates: 5F-PB-22 and its ten isomers

Differentiation among regioisomers of synthetic cannabinoids in forensic drug analysis is a crucial issue, since all isomers are not regulated by law. New equivalent analogs obtained via minor modification of their preexisting molecules keep on emerging. Isomers formed via substitutional exchange are also a cause for concern. This study is focused on the isomeric molecules that stem from minor modifications of 5F-PB-22. The analytical properties of these molecules and methods of differentiation are reported. Scan mode analysis using gas chromatography–electron ionization-mass spectrometry (GC–EI-MS) was performed using the authentic 5F-PB-22 standard, five regioisomeric quinolinyl ester indoles, and five regioisomeric isoquinolinyl ester indoles. Because it was not possible to separate 5F-PB-22 from the 5-hydroxyquinoline isomer using GC and all analytes showed similar EI mass spectra, liquid chromatography (LC)–tandem mass spectrometry analysis was performed. Using LC, a successful separation of 5F-PB-22 from all isomers could be achieved. Based on the electrospray ionization-mass spectra, the protonated molecular ion at m/z 377.2 was selected as the precursor ion for the regioisomeric and structural isomeric differentiation. Collision-induced dissociation provides relative intensity differences in the product ions among the isomers, enabling mass spectrometric differentiation of the isomers. To our knowledge, this is the first report on mass spectrometric differentiation of 5F-PB-22 and its ten isomers.