Ionic liquids as stationary phases for the gas chromatographic separation of fentanyl analogues

•Fentanyl analogues synthesized via the Gupta method were analyzed using the IL column.•Separation of fentanyl, 22 analogues and U-47700 is possible using an IL column.•IL phase provides better separation than 5% diphenyl/95% dimethylpolysiloxane phase.•2 to 25% increase in selectivity was observed using an ionic liquid column.•Method can discriminate analogues in drug samples containing a number of impurities.