Patent ID: 7815783

Claim:
A filter apparatus comprising: (a) a central reservoir configured to contain a sample; (b) at least a first, a second, a third, and a fourth satellite reservoir in fluid communication with the central reservoir; (c) at least a first, a second, a third, and a fourth portal joining a corresponding one of the at least first, second, third and fourth satellite reservoirs with the central reservoir; (d) at least a first, a second, a third, and a fourth filtration device, differing from each other in pI-selectivity, wherein the first, second, third, and fourth filtration devices are positioned in the first, second, third, and fourth portals, respectively, wherein the first filtration device is either a highest-pI-selective or a lowest-pI-selective filtration device and the second filtration device is the other of the highest-pI-selective or the lowest-pI-selective filtration device, and wherein the third filtration is either a higher-pI-selective or a lower-pI-selective filtration device and the fourth filtration device is the other of the higher-pI-selective or the lower-pI-selective filtration device wherein the first, second, third and fourth filtration devices comprise a member independently selected from an isoelectric bead bed and a zwitterionic packed particulate material wherein the isoelectric bead bed comprises porous beads coated with a passivating layer, wherein the porous beads are filled with a substance comprising a predetermined isoelectric point; and (e) at least a first electrode configured to be in electrical contact with the first satellite reservoir, a second electrode configured to be in electrical contact with the second satellite reservoir, a third electrode configured to be in electrical contact with the third satellite reservoir, and a fourth electrode configured to be in electrical contact with the fourth satellite reservoir, wherein the first and the second electrodes are oppositely charged, wherein the first and the second satellite reservoirs are oppositely positioned across the central reservoir, wherein the third and the fourth electrodes are oppositely charged, and wherein the third and the fourth satellite reservoirs are oppositely positioned across the central reservoir, wherein in a first separation step, the first and second electrodes are configured to be charged so that molecules move through the highest-pI-selective and lowest-pI-selective filtration devices and into the first and second satellite reservoirs, and wherein after the first separation step, the first and second electrodes are configured to be de-charged and the third and fourth electrodes are configured to be charged so that molecules move through the higher-pI-selective and lower-pI-selective filtration devices and into the third and fourth satellite reservoirs, thereby leaving molecules having pI values between the pI-selectivities of the higher-pI-selective and lower-pI-selective filtration devices in the central reservoir.