Archimedean screw generator

The basic hydrodynamic equilibrium system (Fig. 1, right) uses a rotating coil which generates an Archimedean screw effect where all objects in different density present in the coil are driven toward one end, conventionally called the head. The mobile phase introduced through the head of the coil is mixed with the stationary phase to establish a hydrodynamic equilibrium, where a portion of the stationary phase is retained in each turn of the coil. This process continues until the mobile phase elutes from the tail of the coil. After the hydrodynamic equilibrium is established throughout the coil, the mobile phase displaces only the same phase, leaving the other phase stationary in the coil. Consequently, solutes introduced locally at the head of the coil is subjected to an efficient partition process between the two phases and separated according their partition coefficients. 

Retention of the stationary phase in the coiled column of the HSCCC system totally relies on the Archimedean screw force generated by the planetary motion of the column. However, this force is often too weak to retain the stationary phase for some polar solvent systems, such as aqueous-aqueous polymer phase systems, resulting in carryover of the stationary phase from the column. 

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