– Sodium Citrate Buffer, 0.1M, pH 4.0, is a widely used buffer solution composed mainly of citric acid and disodium hydrogen phosphate. It is utilized for heat-induced epitope retrieval (HIER) to restore the antigenicity of certain epitopes that may be lost in formalin-fixed, paraffin-embedded tissue. This buffer is the preferred solution for most antibodies and can also be employed for the hydration of liposome membranes.