Washing with water (28 mL) was then performed in the same fashion. Both the extraction of [ 18 F]FSPG and washing steps were performed by loading onto the female end of the cartridge. Syringe 3 was used to pass the PBS eluent through the two MCX SepPak cartridges in a 'reverse elution', passing in the opposite direction to which the MCX SepPak cartridges were loaded and washed. The product was eluted through an Alumina light SepPak cartridge and an altered Hypercarb cartridge before collection in a glass vial. The optimized FASTlab sequence is provided in the supplementary materials.