Sodium bicarbonate functions as a mild buffer and neutralizing agent in biochemical protocols, particularly for pH adjustment in enzymatic reactions, cell culture media, and DNA electrophoresis due to its amphoteric nature and CO₂ evolution for gentle acidification.
Chemical Properties
Sodium bicarbonate (NaHCO₃, MW 84.01 g/mol) forms a white monoclinic crystalline powder (density 2.20 g/cm³, decomposes at 50°C) consisting of Na⁺ cation and HCO₃⁻ anion. The bicarbonate features a planar carbon with three oxygen atoms (two equivalent, one H-bonded). It is moderately soluble in water (9.6 g/100 mL at 20°C) and establishes buffer equilibria:
HCO₃⁻ ⇌ H⁺ + CO₃²⁻ (pKa₁ 6.35)
H₂CO₃ ⇌ H⁺ + HCO₃⁻ (pKa₂ 10.33), yielding pH 8.3 for 0.1 M solutions via hydrolysis:
HCO₃⁻ + H₂O ⇌ H₂CO₃ + OH⁻
Biochemical Applications
In molecular biology, 50–100 mM NaHCO₃/Na₂CO₃ (pH 9.6) is used for passive adsorption of proteins or DNA to ELISA plates or nitrocellulose membranes. Enzymology applies 25–100 mM in TAE/TE buffers (pH 8.0–8.3) for agarose gels, minimizing heat generation during electrophoresis. In cell culture, 2–10 mM is combined with 5–10% CO₂ incubation to maintain physiological pH (7.2–7.4), matching blood buffering. Protein refolding protocols leverage slow CO₂ bubbling for gradient acidification (pH 8 → 6). It also neutralizes alkaline lysates in plasmid minipreps without NaOH carryover.
