The radiotracer (100-200 kBq, [ 18 F]1c or [ 18 F]1f) in PBS (2 µL) was incubated with human plasma (100 µL) at 37 °C for 10 min. After preconditioning of the microcolumns according to the instructions of the manufacturer (illustra MicroSpin G-50 columns from GE Healthcare), a sample (40 µL) of was applied to the resin. The microspin tubes were centrifuged (2,000 g, 2 min) and both, eluate and resin were supernatant were mixed with 600 µL methanol including 50 ng/mL clopidogrel-d3 as an internal standard. Samples were centrifuged, the solvent of 600 µL supernatant was evaporated to dryness and 100 µL mobile phase was used for reconstitution. The injection volume was 5 µL. All experiments were performed with eight biological replicates. Unpaired t-test was used for analyzing differences with p-values <0.05 considered significant.