A novel method for protein purification was presented

which was the integration of organic antisolvent and compressed gas isoelectric precipitation.In this work the study on isoelectric precipitation of BSA in the compressed carbon dioxide-aqueous system was carried out using ethanol as a precipitation assistant and CO2 as a volatile acid.The precipitation was obvious and it proved that ethanol played two roles in the system.Firstly，ethanol facilitated BSA precipitation at the isoelectric point.Secondly

it reduced the buffer capacity of BSA.This resulted in a decrease of the pressure that was required to reach the isoelectric point so that precipitation could be attained with an increase of maximum BSA concentration that could be acidified to the isoelectric point.Furthermore，the BSA stability in the above processes was investigated

it was shown that there were no irreversible changes in the conformation of BSA

and BSA existed stably in all cases involved.All the experiments indicated that the improvement provided the novel system with an upper hand over the system reported before.The results would be helpful for the development of protein separation and purification techniques.