The invention relates to a method and an apparatus (100) for the enrichment of magnetic particles (1) in a sample fluid. The sample fluid is provided in a sample cartridge (2) between a first pole (111) and a second pole (112) of an actuator magnet (110). A minimal magnetic flux as well as a minimal magnetic gradient are then established inside the sample fluid, wherein their values depend on the particular magnetic particles (1) and the sample fluid under consideration. In a preferred embodiment, the first pole (111) has a single tip (T).