Hybrid magnetic field gradient, rotating wall device for enhanced colloidal magnetic affinity separations
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. The separation is demonstrated on a model feed system consisting of a mixture of 1.0 μm diameter biotinylated latex beads (targets) and 9.7 μm diameter non-functionalized latex beads (non-targets) at a 1:1 number ratio. Two feed flow rates of 12 ml/min and 35 ml/min were used until a total of 600 ml of sample were processed for each. At the low rate we achieved capture efficiency 60%, a separation factor of 18.2 with 95% purity. For the higher flow rate, the capture efficiency was 40%, the separation factor 18.6 with 87% purity. ^ The same device also was used for removal of cadmium ions from a cadmium sulfate solution. Two arrangements for the magnetic units were used. In the first configuration, four hybrid pairs were distributed axially—each pair consisted of an alternating current carrying solenoid, followed by four azimuthally distributed permanent magnets that rotate with the chamber. In the second configuration, all four solenoids were placed first, followed by the four sets of four azimuthally distributed permanent magnets. 1–10 μm diameter magnetic particles with iron oxide nanoparticles embedded within a quaternary ammonium cellulose matrix (MagaCell-Q, Cortex Biochem) at a starting concentration of 0.5 mg particles/mL were used as the mobile solid support. The feed consisted of a 10.0 mg/L cadmium sulfate solution, at a flow rate of 35 mL/min. For the arrangement, the cadmium concentration at the exit of the third stage dropped to 0.97 mg/L. The second configuration produced a final cadmium concentration of 0.68 mg/L. For the first arrangement, three stage processing resulted in an overall ∼90% w/w cadmium removal, and the second configuration removed ∼94% of the original cadmium ions. The operating mode of this device requires a periodic interruption of the feed flow, leading to down time. Thus there is a compelling motivation to the development of the continuous device. ^ The continuous, hybrid magnetic field gradient separation device, designed in our lab, incorporates a 1.0 cm internal diameter 1m long, axially-rotating horizontal glass tube, with four axially located repeating magnetic units. Each magnetic unit consists of an alternating current solenoid surrounding the chamber followed by electromagnets at a distance of 4.0 cm from the end of the solenoid. A computer controlled DC current flowing in the electromagnet is used to generate radial magnetic field gradients within the tube, allowing magnetic particles to be drawn to the walls. MagaCell-Q magnetic particles were used to demonstrate the removal of cadmium ions from an aqueous solution. Three stage processing resulted in an overall ∼92% cadmium removal. Thus, this breakthrough technology in continuous separation can lead to a large increase in processing volume and reduced down time compared to the flow-through device, without loss of removal efficiency. ^ While the specific system studied here consists of removal of cadmium ions from an aqueous solution, the general principle of magnetic colloidal separation using the flow-through and continuous devices can be exploited for other environmental and biotechnological applications where large volumes of sample must be processed with high efficiency. ^
Biology, Cell|Engineering, Chemical|Physics, Electricity and Magnetism
Alazar Negusse Ghebremeskel,
"Hybrid magnetic field gradient, rotating wall device for enhanced colloidal magnetic affinity separations"
Dissertations and Master's Theses (Campus Access).