Direct tissue sampling of diazepam and amitriptyline using mixed-mode SPME fibers: A feasibility study

•Sorption from tissue to a novel mixed-mode or C18/SCX fiber is described.•Diazepam was tested as model neutral compound, amitriptyline as cationic compound.•Uptake of the test compounds from agarose gel and tissue was fast and sensitive.•Changes in matrix tortuosity and rate of diffusion did not decrease fiber uptake.