Desalting, Concentration, and Buffer Exchange by Dialysis and Ultrafiltration

This unit includes a variety of dialysis and ultrafiltration techniques that can be used for desalting, concentration, or buffer exchange. Standard dialysis by diffusion across cellulose tubing is described as a technique for desalting or buffer exchange. Ultrafiltration under pressure can be used either for concentrating protein or, where the sample volume is replenished with a desired buffer, for desalting/buffer exchange (i.e., diafiltration). A variation is ultrafiltration by tangential flow, which serves the same purposes as ultrafiltration under pressure but is better suited to handling large volumes of solution. Yet another variation is an ultrafiltration technique employing centrifugal microconcentrators, which allows concentration of very small volumes of solution.