The present invention relates to a liquid mixture comprising a first polymer, which is a poly(acid), a second polymer, which is a poly(ether), and at least one salt, wherein the molecular weight of the poly(acid) is in the range of 1000-100,000 Da. The second polymer is selected to be capable of forming immiscible aqueous phases in the presence of the poly(acid) and salt. The poly(acid) may be selected from the group consisting of poly(acrylic acid) and poly(methacrylic acid), and the second synthetic polymer may comprise ethylene oxide. The invention may be used for separation of biomolecules, cells or particles.