Britton Robinson buffer

Britton–Robinson buffer (aka BRB aka PEM) is a "universal" pH buffer used for the range pH 2 to pH 12. Universal buffers consist of mixtures of acids of diminishing strength (increasing pK_a) so that the change in pH is approximately proportional to the amount of alkali added. It consists of a mixture of 0.04 M H₃BO₃, 0.04 M H₃PO₄ and 0.04 M CH₃COOH that has been titrated to the desired pH with 0.2 M NaOH. Britton and Robinson also proposed a second formulation that gave an essentially linear pH response to added alkali from pH 2.5 to pH 9.2 (and buffers to pH 12). This mixture consists of 0.0286 M citric acid, 0.0286 M KH₂PO₄, 0.0286 M H₃BO₃, 0.0286 M veronal and 0.0286 M HCl titrated with 0.2 M NaOH.