Method and arrangement (10, 20) for preparing samples (15, 27) submergible in a liquid medium. The arrangement includes a carrier structure (11). The carrier includes a device (13, 23) for controllable generation of a magnetic field through influence of a control signal to attract at least part of the at least first and second type of samples (15, 27) towards specific locations on the carrier when connected to a first control signal and to repel at least one of the first or second type of samples when connected to a second control signal.