A flow-through, hybrid magnetic-field-gradient, rotating wall device for magnetic colloidal separations

Document Type


Date of Original Version



A 2.0 cm internal diameter 1 m long, axially-rotating horizontal glass tube, with four axially located repeating hybrid magnetic units, is used as part of a flow-through, colloidal magnetic affinity separation device. Each magnetic unit consists of an alternating current solenoid surrounding the chamber followed by four azimuthally distributed permanent magnets that rotate with the chamber. Experiments were carried out on a model feed system consisting of a mixture of 1.0 μm diameter biotinylated latex beads (targets) and 9.7 μm diameter nonfunctionalized latex beads (nontargets) at a 1:1 number ratio. Streptavidin labeled magnetic particles (2.8 μm diameter polystyrene - Dynabeads) at a number concentration of ˜3 x 106 beads/mL were used as the separation vehicles. Two feed flow rates of 12 and 35 mL/min were used until a total of 600 mL of sample were processed for each. At the low rate we achieved a capture efficiency of 60 ± 4% and a separation factor of 18.2 ± 1.2 with 95 ± 4% purity. For the higher flow rate the capture efficiency was 40 ± 4% and the separation factor was 18.6 ± 1.5 with 87 ± 4% purity. A single stage batch process, where a total of 10 mL of feed was processed at identical feed and magnetic bead concentrations required ˜2 hours, produced a capture efficiency of 42 ± 4% and a separation factor of 3.8 ± 1 with 79 ± 4% purity. Three batch stages (2 hours processing time per stage) were required to surpass the capture efficiency of the flow-through device at the smaller flow rate. Thus, this flow-through separation device can lead to a large increase in processing volume and reduced ’down’ time, compared to current batch processes, without loss of either efficiency or purity, potentially opening up magnetic colloidal separations for large scale applications.

Publication Title

Separation Science and Technology