β = ΔC / ΔpH
Buffer capacity (β) measures a buffer's resistance to pH change when acid or base is added. β = 2.303 × C × Ka × [H⁺] / (Ka + [H⁺])². Maximum buffer capacity occurs when pH = pKa (where [HA] = [A⁻]). A buffer is effective within ±1 pH unit of its pKa. Increasing total buffer concentration increases β linearly. For example, a 0.1 M phosphate buffer at pH 7.2 has about 4× the capacity of a 0.025 M buffer. Blood is buffered at pH 7.4 primarily by the carbonic acid/bicarbonate system (pKa 6.1) — despite being outside the ideal range, its effectiveness comes from the body's ability to regulate CO₂ (volatile acid) through breathing. Laboratory buffers commonly used: acetate (pKa 4.76), phosphate (pKa 7.2), Tris (pKa 8.1), and carbonate (pKa 10.3).