The Oasis WAX Plus cartridges contain the Oasis WAX sorbent, which is a polymeric reversed-phase, weak anion exchange mixed-mode sorbent that has been optimized for fast, simple, and highly selective sample preparation of strong basic compounds and quaternary amines. Since the Oasis WAX sorbent is water wettable, it is used to retain and release strong acids and is stable in organic solvents.