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Posted on Tue, Jan 29, 2013

The 2 basic points for understanding how magnetic separation works


Magnetic bead separation is widely used in IVDSeparation techniques using magnetic carriers (either beads or particles) are often used in the life sciences to ‘capture’ specific biomolecules. These techniques utilize immunocapture, DNA fragments, or electrical charge in order to specifically target the biomolecule of choice. After magnetic capture of the biomolecule, magnetic forces can separate it from the rest of the milieu. Because of the seeming ease of separation, biomagnetic techniques are used by some as the ‘gold standard’ of separation technology.

This post is about magnetic bead separation and how to validate this process. If you are interested in this topic, and are willing to learn more about it, download our Free Guide The Starting Guide to Validate Biomagnetic Separation Processes:

Free PDF guide:   "Validation of Magnetic Bead Separation Processes" 

While magnetic bead separation does have clear advantages over other techniques (e.g. centrifugation, filtration, affinity chromatography, gel purification, etc.) for purifying biomaterials, one needs to have a very good understanding of the physical principles behind magnetic separation in order to implement the technique correctly.

Understanding how magnetic separation works

Two basic points are necessary for understanding magnetic separation:

1. Magnetic forces are generated by non-homogeneous magnetic fields

  • A homogeneous magnetic field torques, but does not generate a force over a magnetic moment.
  • A magnetic force, however, is created by varying the magnetic field over a defined area (spatial variation).
  • A single permanent magnet separates because it generates a large spatial variation in its magnetic field, not because it generates a high magnetic field.

2. The value of the magnetic force depends on the magnetization of the beads

  • The force of the magnetic field can be expressed as:
Field force in magnetic bead separation
  • If the magnetic bead has a magnetic moment that varies (i.e. a linear response with a constant susceptibility), the magnetic moment will be χVH and the value of the force will depend on how it changes the square of the magnetic field: B2. (H=B/µ0):
Magnetic moment in magnetic bead separation
  • If the magnetic bead has a constant magnetic moment (ms), the force depends on the magnetic field gradient:
Field gradient in magnetic bead separation
  • The magnetization of the beads will be linear at low magnetic fields and saturated at high magnetic fields.


The ability to understand how magnetic fields and beads interact, how magnetic forces are generated and how magnetic forces drive the beads against the viscosity of the suspension are key facets of knowledge to having reproducible, efficient and problem-free magnetic bead separation.

It is important for scientists to understand both the spatial profiles of the magnetic field generated by the separation device and the magnetization curve of the magnetic beads. Once these variables and basic principles are mastered, one can create a much more robust purification process.

Bead behavior in magnetic bead separationIf you found this article interesting and want to get a deeper insight in the topic of magnetic bead separation, make sure to check these articles from our blog:

Dr. Lluís Martínez

biomagnetic separation processes

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