Cryopartitioning in Two-Phase Systems Containing Organic Solvents

Aqueous two-phase systems, based on two polymers, usually freeze at temperatures below -1�C. The freezing point can be considerably lowered by exchanging part of the water for a water miscible organic solvent such as ethylene glycol or glycerol (1 ). Partitioning of proteins and particles has been carried out in such systems using temperatures down to -20�C (2 ,3 ). The low temperature, in combination with the solvent, gives the phases high viscosity, which influences the time for equilibration and especially the time for phase separation. Sometimes centrifugation at the equilibration temperature is advisable.