Citratpuffer

Citratpuffer, commonly called citrate buffer in English, is a buffer solution based on citric acid and its conjugate base salts, typically trisodium citrate or potassium citrate. It is used to maintain a stable pH in biochemical and analytical procedures.

Citric acid is triprotic, with dissociation constants around pKa1 3.13, pKa2 4.76, and pKa3 6.40. Because of these multiple pKa values, citrate buffers can operate effectively over a broad pH range, roughly 3 to 6.5. The exact pH is set by the relative amounts of citric acid and citrate base and can be tuned for specific applications.

Preparation and composition typically involve dissolving citric acid and a citrate salt in water, then adjusting to the desired pH. The ionic strength can be modified with additional salts such as NaCl. Final concentrations commonly range from about 10 mM to 200 mM, depending on the required buffering capacity.

Applications include maintaining pH in enzymatic reactions, protein purification and characterization, chromatography and immunoassays, and certain electrophoretic or crystallization contexts. Citrate buffers are often chosen for their affordability and compatibility with many biological systems, though the citrate ion can chelate divalent metal ions such as Mg2+ or Ca2+, which can influence enzyme activity or cofactors.

Storage and safety notes: citrate buffers are generally stable at room temperature but should be protected from contamination and metal ions. They are low hazard under normal laboratory handling, with standard safety precautions.