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.
This post is about biomagnetic 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 Biomagnetic 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.
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 biomagnetic separation systems is never straightforward. Thankfully, modern homogeneous biomagnetic 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 biomagnetic separation processes:
- Why Do Larger Batches Not Have the Same Characteristics as Smaller Batches?
- Why do Larger Non-Homogeneous Magnetic Separators Have Higher Losses of Magnetic Beads and Biomolecules?
- Why are there More Magnetic Bead Irreversible Aggregation Problems in Non-Homogeneous magnetic separators