All the solutions used in this simulation consist of a buffer and salt (sodium chloride) in water. In practice, it is often desirable to include other additives to the mobile phase for protein separations, such as bacteriostatic agents.
In preparing the mobile phase, the buffering agent is used at a concentration of 20 - 100 mM (0.02 - 0.10 M) and the pH is adjusted, usually with concentrated acid or base. The buffer is selected so that the target pH of the mobile phase is close to the pKA for the buffer. It is also possible to mix a buffer at a given pH by mixing the proper ratio of the acid and base forms of a weak acid or base (see Buffers).
In ion exchange chromatography the binding and elution of protein is controlled by pH (which controls the charge on the protein and the stationary phase) and the salt concentrations. A bound protein can be released from the stationary phase by changing the pH of the mobile phase, or by increasing its salt concentration.