Principles of Magnetic Separation

Magnetic separation is the process where magnetically susceptible material is extracted from a mixture using a magnetic force. Magnetic separations are utilized in many areas of research, particularly in the biotech and pharma industries, for the purification, isolation, and separation of a particular entity such as cells or proteins. The “capturing” or magnetic separation of said entities from complex media is crucial to fundamentally study the traits and characteristics of the isolated material in a research environment.

To be fully versed in magnetic separation technology, one must be educated in not only the magnetics used in the separation but the varied forms of magnetism that a material, such as a magnetic liquid, can possess. To “capture” a magnetically labeled cell a magnetic gradient (i.e. a change in the magnetic flux line density) as a function of distance is required. Magnetic gradients result from magnetic circuits – the flow of field lines from North (N) to South (S) poles. Thus, a simple bar magnetic (attractive force) near its poles as a result of the flowing from N-to-S poles creates a non-uniform magnetic field (the flux lines are not equivalent). When a magnetic material interacts with the magnet field from a bar magnet, the material is “attracted” to the magnet. This phenomenon can be equated to the “pull” you feel when placing a magnet on a refrigerator.

Now all materials, man-made or in nature, are influenced to some extent by a magnetic field. There are three forms of magnetic materials: (1) Diamagnetic (2) Paramagnetic and (3) Ferromagnetic. (1) Diamagnetic materials create a magnetic field in opposition to an externally applied magnetic field. These materials are generally referred to as non-magnetic, as they are repelled or not attracted to a magnetic surface. Some simple examples are wood, plastic, and heavy metallic objects such as mercury or gold. (2) Paramagnetic materials are attracted by an externally applied magnetic field. These materials are comprised mostly of chemical elements with an odd number of electrons resulting in one electron that is termed “unpaired”.  Conversely, diamagnetic materials general have an even number of electrons or electrons that are all “paired”. From a research perspective, to be able to magnetically capture a material that is paramagnetic it has to be relative large (sub-micron, 10-6 meters) in size or the external field has to be rather high to attract the material. For these reasons, the researcher is at a disadvantage of using paramagnetic materials in their studies are you would have to use a large amount of material or have a magnet that is not only large in size and rather expensive. However, there are other reasons why one may choose to use a paramagnetic material but there is another option to consider. (3) Ferromagnetic materials also can be attracted to a magnetic field. Ferromagnetism is the strongest type of magnetism and is the only type that creates a force strong enough to be felt. Ferromagnetic materials are a common occurrence in everyday life – remember the refrigerator magnet example? Only a few chemical elements are ferromagnetic (commonly nickel, iron, and cobalt) and most of their alloys are important to modern technology. These materials are the basis for many electromechanical devices such as generators, magnetic storage and hard disks.

In the biotech industry, ferromagnetic materials are advantageous to use in separations as they use less material, reduce costs and can save time permitting the researcher with results in a more timely fashion. Ferromagnetic materials are commonly termed “ferrofluids”: ‘ferro’ for their magnetic properties and ‘liquid’ representing the state of which the material is in. They are colloidal in nature and are suspended in a carrier fluid (usually an organic solvent or water). Ferrofluid particles can be synthesized to varying shapes and sizes but are commonly spherical. Each particle is stabilized at its surface by a surfactant and is the main reason why particles can remain suspended in solution for long periods with little-to-no aggregation. Below is representation of how a ferrofluid can be stabilized with a surfactant.


While magnetic separations are an exceptional analytical tool, their widespread application has been limited by the magnetic particle technology and the design of the separator.

At BioMagnetic Solutions, we have developed more advanced magnetic common capture reagents and engineered a solution to cumbersome and expensive electromagnets for bulk process separations. BioMag’s XpresSepTM multipole separator design generates a highly localized magnetic field enabling the researcher to work with smaller volume of material and achieve the results germane to their work. Our team is continually working on improving our technology to provide more quantitative results to assist bench-top researchers to batch separation processes. To learn more about how magnetic separation technology can assist your research efforts check out our Products pages or contact us directly to get the answers you need to solve your research efforts.