Good's Buffers - Selection Criteria

Selection Criteria

Good sought to identify buffering compounds which met several criteria likely to be of value in biological research.

1. pK_a. Because most biological reactions take place at near-neutral pH between 6 and 8, ideal buffers would have pK_a values in this region to provide maximum buffering capacity there.
2. Solubility. For ease in handling and because biological systems are in aqueous systems, good solubility in water was required. Low solubility in nonpolar solvents (fats, oils, and organic solvents) was also considered beneficial, as this would tend to prevent the buffer compound from accumulating in nonpolar compartments in biological systems: cell membranes and other cell compartments.
3. Membrane impermeability. Ideally, a buffer will not readily pass through cell membranes, this will also reduce the accumulation of buffer compound within cells.
4. Minimal salt effects. Highly ionic buffers may cause problems or complications in some biological systems.
5. Influences on dissociation. There should be a minimum influence of buffer concentration, temperature, and ionic composition of the medium on the dissociation of the buffer.
6. Well-behaved cation interactions. If the buffers form complexes with cationic ligands, the complexes formed should remain soluble. Ideally, at least some of the buffering compounds will not form complexes.
7. Stability. The buffers should be chemically stable, resisting enzymatic and non-enzymatic degradation.
8. Optical absorbance. Buffers should not absorb visible or ultraviolet light at wavelengths longer than 230 nm so as not to interfere with commonly-used spectrophotometric assays.
9. Ease of preparation. Buffers should be easily prepared and purified from inexpensive materials.