Centrifugal concentrators, like Vivaspin, are a patented vertical membrane technology, designed for the quickest filtration with highest recovery of target proteins. This makes the Vivaspin the technology of choice for buffer exchange or desalting, avoiding those lengthy dialysis steps. While an ultrafiltration membrane retains proteins, salts are able to pass freely through, independent of protein concentration on membrane MWCO. For more information on how the desalting process works with centrifugal concentrators in your lab, read on!
The Desalting Process
The makeup and composition of the buffer in the flow-through and retentate is unchanged after protein concentration. After diluting the concentrate back to the original volume, salt e concentration is then lowered. The concentrate can then be diluted with water or salt-free buffer if simple desalting is needed. However, it is also quite possible to dilute the concentrate with a new buffer, thereby exchanging the buffering substance whole.
From here, protein samples can then be concentrated again to the desired level, or the buffer exchange could be repeated to reduce the amount of salt concentration even further before a final concentration of the protein. This process is known as “diafiltration.” For proteins with some tendencies to precipitate at much higher concentrations, it is possible to perform multiple diafiltration steps in sequence, with the protein concentrated each time only five or 10x.
Desalting and Buffer Exchange Process
- Pick the most appropriate MWCO for your sample. For maximum recovery, choose an MWCO 1/2 to 1/3 the molecular size of your species of interest.
- Fill the concentrator with up to the maximum volume stated in your device operating instructions.
- If the sample is a bit smaller than the maximum device volume, it can be diluted up to max volume before the first centrifugation step.
- Centrifuge for the recommended time amount at the appropriate spin speed for your Vivaspin centrifugal model.
- Empty the filtrate container
- Refill concentrator with the right solvent
- Centrifuge again like before
- Empty filtrate container
- Recover your concentrated, desalted sample from the bottom of your concentrate pocket with some pipettes.
Efficiency of Vivaspin Devices
The efficient designs of the Vivaspin device allowed 95% of the salt to be removed during the very first step of the centrifugation process. Only one subsequent centrifugation step was required to increase the typical salt removal to 99% with 92% recovery of the samples.
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