A graphene tip coupled with liquid chromatography tandem mass spectrometry for the determination of four synthetic adulterants in slimming supplements

•A Gtip SPE and UPLC–MS/MS was established for determining synthetic adulterants.•Fenfluramine, phenolphthalein, bumetanide, and sibutramine were analyzed.•Graphene was used as sorbent for a microscale SPE using pipette tip as cartridge.•It is good at testing low level contaminates resulted from violation of regulation. Slimming supplements were popularly sold online driven by the increasement of obesity and the development of social networking platform. However, events of drug abuse in slimming supplements were also frequently reported. In this study, a graphene tip solid-phase extraction (Gtip SPE) and ultra-performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS) method was established for determining fenfluramine, phenolphthalein, bumetanide, and sibutramine in slimming supplements. It was validated in terms of linearity (0.9985–0.9995), LOD (1.8ngmL−1), LOQ (5.6ngmL−1), intra-day precision (