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| What makes a good buffer? |
A buffer can maintain the solution pH at a particular value. It can "soak up" the hydronium or hydroxide from added acids and bases, respectively. The value of a buffer is that it can permit chemical reactoins in an environement with a relatively constant [H3O+]. This is extremely important in living cells where biochemical reactions are highly pH sensitive, but it is also necessary for chemical synthesis and other laboratory procedures. Laboratory research frequently involves preparation of buffers in the appropriate pH range for a particular process. The best buffer is one that has a good match between the buffer's acidity constant, i.e. the Ka and the required [H3O+].
The choice of buffer also must take the other chemical compounds in a mixture into consideration. Certain ions are not soluble in combination with other ions. For example, phosphate is a common ion used in buffers, but phosphate and hydrogen phosphate have limited solubility in the presence of divalent metal ions such as Ca2+ or Mg2+. Phosphate buffers are always made with Na+ or K+ ions. If you are adding calcium to the buffer for any reason you many want to use a different buffer. Buffers can also interact with detergents used to isolate mymbrane proteins or specific metal binding sites and so on. There are inorganic buffers (phosphate, sulfate etc.) and organic buffers (citrate, acetate, TRIS, HEPES, MOPS etc.). These are described in the section on buffers.
We can quantify the concentration of an acid or base in solution using a titration. Titrations involve the addition of a known quantity of strong acid to weak base (or strnog base to weak acid) in order to quantify the weak base/acid. We use the known volumes and known concentratoin of the strong acid/base to determine the concnetration of the unknown. Titrations are descrbied in the section on the right.
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