What are the two types of magnetic cell separation?

The two types of magnetic cell separation are column-based and column-free.

Column-Based Magnetic Cell Separation 

In the column-based magnetic cell separation technique, a sample labeled with magnetic particles is passed through a column matrix within a magnetic field. The column contains ferromagnetic spheres that become magnetized in the applied magnetic field, producing a localized magnetic field that can immobilize the magnetic particles within the sample. On using positive selection, target cells that have been labeled with magnetic particles are retained within the column, while non-target cells that are not labeled with magnets can pass through the column. The target cells can be collected by pushing a buffer through the column after removing the external magnetic field. 

Column-Free Magnetic Cell Separation 

In the column-based magnetic cell separation technique, a tube filled with a magnetically-labeled sample is placed within a magnetic field. The target cells, which are magnetically-labeled, migrate towards the magnet and are immobilized at the sides of the tube. The unlabeled cells in suspension can then be pipetted off or poured out to separate them from the labeled cells. The labeled target cells are released from the sides of the tube when the tube is removed from the magnetic field. They can be resuspended in a buffer for immediate use in downstream applications.

Both cell separation methods are useful for isolating specific cell populations from a mixed sample for further analysis or experimentation. Both are well-established techniques that yield highly purified cells. In comparing the two, the column-free cell isolation technique is more efficient as it takes less time and effort to complete the cell separation process.