pH and the Henderson-Hasselbalch equation.
D000136:Acid-Base Equilibrium; D002021:Buffers; D004735:Energy Transfer; D005110:Extracellular Space / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008954:Models, Biological; D010827:Physiology; D013223:Statistics as Topic
D002021:Buffers