What makes a good buffer?

There are many factors that make a good buffer and are listed in the bulleted points below. 

• A pKa of 6-8 - Most biochemical experiments have an ideal pH in the range of 6-8. The ideal buffering range for a buffer is the dissociation constant for the weak acid component of the buffer, plus or minus the pH.
• Minimal salt effects - The buffer components should not affect ions involved in the reactions in the experiment, as high salinity will have a dehydrating effect on cells. 
• Solubility in water - Due to many biological reactions occurring in aqueous environment, it is useful for the buffer to be water-soluble.
• Light absorption - The buffer should not absorb UV light at wavelengths that may be needed for readouts in photometric experiments 
• Non-toxicity - Buffers are often used in research involving living cells, and thus it is necessary for them to be non-toxic to cells in the experiment
• Stability - Buffers are often used on reactions involving enzymes and thus the buffer should be chemically stable enough to resist degradation that enzymes could cause. The buffer should also be resistant to non-enzymatic degradation by other components.
• Well-behaved cation interactions - Many buffers react with cation ligands to form complexes which can amass in different parts of the experiment. Thus, it is important that a buffer only forms a small number of complexes that are soluble, to prevent any amassing
• Membrane impermeability - If a buffer passes through a cell membrane, it will alter the results, thus a good buffer will not pass through membranes.