Factors governing the choice of a buffer

However, there are usually a number of other considerations such as the nature of the reaction system, the ionic strength, the effects of temperature change and dilution, and the possibility of forming insoluble or strongly coloured species or otherwise interacting with components of the solution. For example, the effect of temperature on the pATa of the buffer should be known and, preferably, should not be very large. As pointed out in Chapter 4, this is important for buffers based on Tris (tris(hydroxymethyl)aminomethane) and aliphatic amines. The buffer species should also be chemically stable, should be readily soluble in water and not be readily extracted by organic solvents. 

A good buffer shows little change in pH if there is accidental contamination with acidic or basic materials. For a buffer of the type, BH B + H, acidic contaminants have httle effect if they are weaker acids than BH . Similarly, basic contaminants that are weaker bases than B are not important. For measurements of rates or of physical constants it is often desirable to work under conditions of known low ionic strength. In all cases, the pH of a buffered medium should be determined only after all components have been added and at the temperature of the final measurements. Special requirements for particular buffer applications are discussed below under separate headings. 

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