Sorption of amitriptyline and amphetamine to mixed-mode solid-phase microextraction in different test conditions.

•SPME was explored as rapid direct sampling tool in future bioanalytical application.•C18/SCX and C18 fibers mainly sorb organic cations via adsorption to the C18 surface.•Temperature, ionic strength and agitation influence sorption to the C18/SCX fiber.•Sorption of binary mixtures showed competition effects at high fiber loading.•Careful calibration of the fiber is needed to account for differences in sorption.