In an apparatus for printing images on a moving primary imaging member by jetting ink, containing a fluid and marking particles, in an image-wise fashion onto the primary imaging member, a device for concentrating the ink prior to transferring a marking particle image to a receiver member. The ink concentrating device includes a fractionating unit for separating fluid of the ink from the marking particles. The fractionating unit is located a predetermined spaced distance from the primary image bearing member. An electrostatic field is established between the primary image bearing member and the fractionating unit for concentrating the marking particles in the liquid of the ink.