A particle fractionating apparatus comprising: a charging portion configured to apply voltages to an electrode that is arranged to contact liquid in a flow path for the liquid; a particle detection system configured to detect when no particle will be contained in a droplet produced from the liquid; and a charge controller connected to the charging portion and configured in a first mode to cause the charging portion to apply charge to the liquid so that only the droplet that does not contain a particle will be charged, where the particle detection system comprises a light detector arranged to detect light scattered from the flow path, wherein a signal from the light detector less than a predetermined threshold value indicates the absence of particles, and the charge controller is configured in the first mode of operation to receive from the particle detection system the signal indicating the absence of particles and to apply in response within a predetermined time interval, the voltages to the electrode so that only the droplets that do not contain a particle will be charged, the particle fractioning apparatus further comprising deflecting plates configured to support an electric field between the deflecting plates such that charged droplets that do not contain particles will be deflected by the deflecting plates, characterized in that the charge controller is further operable in a second mode to cause the charging portion to apply charges to droplets produced from the flow path that contain particles such that the charged droplets that contain particles will be deflected by the deflecting plates, wherein the particle fractionating apparatus is configured to be manually switched between the first mode and the second mode. a charging portion configured to apply voltages to an electrode that is arranged to contact liquid in a flow path for the liquid; a particle detection system configured to detect when no particle will be contained in a droplet produced from the liquid; and a charge controller connected to the charging portion and configured in a first mode to cause the charging portion to apply charge to the liquid so that only the droplet that does not contain a particle will be charged, where the particle detection system comprises a light detector arranged to detect light scattered from the flow path, wherein a signal from the light detector less than a predetermined threshold value indicates the absence of particles, and the charge controller is configured in the first mode of operation to receive from the particle detection system the signal indicating the absence of particles and to apply in response within a predetermined time interval, the voltages to the electrode so that only the droplets that do not contain a particle will be charged, the particle fractioning apparatus further comprising deflecting plates configured to support an electric field between the deflecting plates such that charged droplets that do not contain particles will be deflected by the deflecting plates, characterized in that the charge controller is further operable in a second mode to cause the charging portion to apply charges to droplets produced from the flow path that contain particles such that the charged droplets that contain particles will be deflected by the deflecting plates, wherein the particle fractionating apparatus is configured to be manually switched between the first mode and the second mode.