Thermal degradation of a new synthetic cannabinoid QUPIC during analysis by gas chromatography–mass spectrometry

Quinolin-8-yl 1-pentyl-(1H-indole)-3-carboxylate (QUPIC) is a newly introduced synthetic cannabinoid in the drug market. This drug was found to undergo thermal decomposition during gas chromatography–mass spectrometry (GC–MS), probably because of the presence of an ester bond in its structure. Most notably, when QUPIC dissolved in methanol or ethanol was analyzed by GC–MS, most of the QUPIC decomposed to give thermal degradation products. We identified the products as methyl 1-pentyl-(1H-indole)-3-carboxylate, ethyl 1-pentyl-(1H-indole)-3-carboxylate, and methyl indole-3-carboxylate by comparison of their mass spectra with those of reference standards synthesized in our laboratory. Nonalcoholic solvents such as acetone and chloroform gave a major peak and a minor peak for unchanged QUPIC and the degradation product 8-quinolinol, respectively. Furthermore, we studied the effects of various parameters, such as injection methods (splitless or split, and split ratio), injector temperatures, and injector liners on the thermal degradation of QUPIC. Split injection was effective in avoiding degradation. When performing splitless injection, an injector temperature of 250 °C and a surface deactivated injector liner without glass wool minimized the degradation and enhanced the sensitivity. These results indicate that special attention is required for GC–MS analysis of QUPIC, and the information presented in this study will be very useful for forensic toxicologists using GC–MS.