PURPOSE: To separate and concentrate ferritin under optimum separating conditions by subjecting a voltage for migration to feedback control.
CONSTITUTION: A packing material 19 is packed into a hollow column 4 and another packing material 20 is placed thereon. A sample soln. 1 contg. the protein ferritin which is the sample to be separated is added to a carrier liquid 15 and a pump 2 is operated to admit the ferritin into the column. A power source 11 for electrophoresis is then operated and a positive electrode 14 is set in the upper part of the column and a negative electrode 13 in the lower part to provide a voltage gradient into the column. Only the carrier liquid 15 is added to the column when the addition of the ferritin ends. A voltage difference between the electrodes 12 and 12' disposed near the boundary of the two packing materials is measured by a voltage measuring instrument 3 through signal lines 8, 9. The concn. of the separated ionic material is known by measuring the voltage gradient in the column. The voltage for migration is controlled by the result thereof, by which the sepn. is executed at a high speed under the optimum conditions.