Keep the cartridge fixed on the vacuum manifold and place a rack inside the vacuum manifold setup and it vials into it. Cover the manifold by the lid containing dried cartridge. Then, put a syringe body (without piston) on the top of the cartridge and add 4 mL methanol (LC/MS grade) and follow by 2 mL acetonitrile. Wait until all acetonitrile pass through the cartridge and then turn on the vacuum pump for 3 min to pumping the residual