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Why Can’t You Simply Use a Bigger Magnet to Scale-Up Magnetic Bead Separation Processes?

By 19 de September de 2013June 14th, 2024No Comments

While it might be thought that ‘bigger is better’ during a scale-up process, merely using a larger magnet in a magnetic separation rack for larger volumes generates very different conditions. This leads to inconsistencies and other problems with the final product.

Download our Free Guide on Biomagnetic Separation Scale-up HERE.

This post is about Magnetic Bead Separation with a magnetic separation rack, and how to scale-up this process. If you are interested in this topic, download our free eBook The Basic Guide to Scale-up Magnetic Bead Separation Processes:

Working with a small magnetic separation rack

In small working volumes, acceptable conditions are worked out, but when scaling up, those conditions do not seem to work well. Specifically, when one looks at the gradient of the magnetic field, the magnitude of the gradient is related to the magnetic force when the beads are saturated.

This gradient will vary greatly with the size of the magnet and the volume of the sample. For example, if the beads are in a 5 cm bottle (diameter), and a small magnet (with dimensions = 2 x 1 x 0.5 cm) is used as magnetic separation rack, the magnetic force would be between 3 and 5 T/m.

magnetic separation rack force variations

Increasing magnetic separation rack volume

When working with a larger volume, such as a bottle with a diameter of 10 cm (~four times the volume of the above example), there is a temptation to use a larger magnet as magnetic separation rack, in order to counter the larger volume. If the magnet has dimension of, for example, 4 x 2 x 1 cm, the magnetic force experienced by the farthest beads from the magnet would be slightly more than 1.5 T/m and would never exceed 2.5 T/m.

This is always below the minimum value of the smaller volume example. Even if you increase the magnet size even further (e.g. 8 x 4 x 2 cm), this will not help because the force will be even weaker.

Therefore, just increasing the size of the magnet will not help separate beads in larger volumes. This is a problem that must not be solved by increasing the magnetic field, but must be solved by increasing the gradient of the magnetic field.

Because of this problem, scaling up of non-homogeneous Magnetic Bead Separation systems is never straightforward. Thankfully, modern homogeneous Magnetic Bead Separation systems solve this problem because the magnetic force is well-defined.

Don’t forget to check these posts from our blog in order to get a deeper insight into the scaling-up of Magnetic Bead Separation processes:

Check to access to FREE eBooks on the subject, or contact us. We will be glad to help you to achieve an efficient magnetic bead separation process!

magnetic separation rack

Lluis M. Martínez | SEPMAG Chief Scientific Officer

Founder of SEPMAG, Lluis holds a PhD in Magnetic Materials by the UAB. He has conducted research at German and Spanish academic institutions. Having worked in companies in Ireland, USA and Spain, he has more than 20 years of experience applying magnetic materials and sensors to industrial products and processes. He has filed several international patents on the field and co-authored more than 20 scientific papers, most of them on the subject of magnetic particle movement.

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