New small-scale cross-axis coil planet centrifuge: The design of the apparatus and its application to counter-current chromatographic separation of proteins with aqueous–aqueous polymer phase systems

The cross-axis coil planet centrifuge (X-axis CPC) is useful for partitioning macromolecules with aqueous–aqueous polymer phase systems. The floor model we have built with a pair of separation columns had some shortcomings such as requirement of large space, short life of the flow tubes, and difficulty in installing columns. In order to improve the partition efficiency and the utility of counter-current chromatography (CCC), a new small-scale X-axis CPC was designed and fabricated in our laboratory. The down-sizing of the apparatus was done by reducing the scale to about 1/2 of our original model of X-1.5 L type with several improvements. Performance of the apparatus was evaluated on protein separation using an aqueous–aqueous polymer phase system composed of polyethylene glycol 1000 and dibasic potassium phosphate with four multilayer coiled columns. A series of experiments revealed that the combination of right- and left-handed coils produced the best partition efficiencies for both lower and upper mobile phases by selecting the revolution direction. The overall results indicate that the head–tail elution mode substantially affects to the peak resolution and stationary phase retention. This new X-axis CPC would be useful for the separation of various kinds of biologically active compounds.