In this paper the importance of correct impedance matching is discussed in dielectrophoresis (DEP) experiments with commercial signal generators. An uncompensated and a 50 Ohms terminated setup are compared to an approach utilizing an active in-line buffer with low output impedance. The losses in effective signal amplitude are simulated for different electrode areas with saline fluids. A separation experiment is performed using a single electrode pair with 10 um polystyrene microspheres. The separation capability decreases drastically for larger electrode areas for the uncompensated and the 50 Ohms terminated setups but proper and constant behavior is found for the active buffer configuration.