.Physiomodel.Electrolytes.AcidBase.Buffers.Phosphates

pKa1=2.1, pKa2=6.8, pKa3=12.7   (wiki:  2.12, 7.21, 12.67 at 25°C)

tPO4 = [H3PO4] + [H2PO4] + [HPO4] + [PO4]

charge(tPO4,pH) = [H2PO4] + 2[HPO4] + 3[PO4]

[H2PO4] / [H3PO4] = 10^(pH-pKa1)

[HPO4] / [H2PO4] = 10^(pH-pKa2)

[PO4] / [HPO4] = 10^(pH-pKa3)