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Buffer capacity falls to 33% of the maximum value at pH = pK a ± 1, to 10% at pH = pK a ± 1.5 and to 1% at pH = pK a ± 2. For this reason the most useful range is approximately pK a ± 1. When choosing a buffer for use at a specific pH, it should have a pK a value as close as possible to that pH. [2]
The following table presents pK a values at 20 °C. Values change by about 0.01 per degree of temperature. [1] [3] Good's original 1966 paper had two older buffers (marked with italics) for comparison. In 1972 Good published a second list with three more buffers, and five more were added in 1980.
The Britton–Robinson buffer (BRB or PEM) is a "universal" pH buffer used for the pH range from 2 to 12. It has been used historically as an alternative to the McIlvaine buffer , which has a smaller pH range of effectiveness (from 2 to 8).
Add 2.84 mM of HCl to shift the buffer to 7.3 mM HPO 4 2− and 4.6 mM H 2 PO 4 − for a final pH of 7.4 and a Cl − concentration of 142 mM. The pH of PBS is ~7.4. When making buffer solutions, it is good practice to always measure the pH directly using a pH meter. If necessary, pH can be adjusted using hydrochloric acid or sodium hydroxide.
McIlvaine buffer is a buffer solution composed of citric acid and disodium hydrogen phosphate, also known as citrate-phosphate buffer. It was introduced in 1921 by the United States agronomist Theodore Clinton McIlvaine (1875–1959) from West Virginia University , and it can be prepared in pH 2.2 to 8 by mixing two stock solutions.
Borate buffered saline (abbreviated BBS) is a buffer used in some biochemical techniques to maintain the pH within a relatively narrow range. Borate buffers have an alkaline buffering capacity in the 8–10 range. Boric acid has a pK a of 9.14 at 25 °C.
The pH (and pK a at ionic strength I≠0) of the buffer solution changes with concentration and temperature, and this effect may be predicted using online calculators. [2] MES is highly soluble in water. The melting point is approx. 300 °C. MES was developed as one of Good's buffers in the 1960s.
MOPS (3-(N-morpholino)propanesulfonic acid) is a buffer introduced in the 1960s, one of the twenty Good's buffers. It is a structural analog to MES, [1] and like MES, its structure contains a morpholine ring. HEPES is a similar pH buffering compound that contains a piperazine ring.
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