the body's weak acids:
albumin, phosphate and citrate
among all the substances physiologically occurring in human extracellular fluid, albumin is by far the
most prevalent weak acid, under normal conditions contributing about 12mEq/l of negative charge.
phosphate is a far second, with about 1,8mEq/l. citrate is, according to James Figge (in Stewart's Textbook of Acid-Base, 2009
re-edition by Kellum and Elbers, advertised on this website, page 226) present in amounts of around 0.135mmol/l, with some 0.4
mEq/l negative charge.
everything else - globulins or citric acid cycle intermediates come to mind - has no practical
for a detailed discussion of the weak acids and their physicochemical properties you can turn to
you can calculate the negative ionisation of albumin, phosphate and citrate for different pH values (as well as the ionisations of
citrate, lactate and trometamol)
by following this link! - with a lot more information about the calculations.
haemoglobin gets often mentioned in the context of "buffer bases", to use this common expression from
the Siggaard-Andersen terminology.
according to the Stewart approach, haemoglobin cannot possibly contribute to the acid-base
analysis of extracellular fluid (ECF), because it is found almost exclusively inside of erythrocytes, all the independent values
already having been measured, independently of what the influence of haemoglobin may be. haemoglobin has an important influence on
whole blood, though, which becomes important when titrating whole blood, but, as already mentioned, is irrelevant, once the usual
measurements have been made. this is further discussed in the section on haemoglobin's influence.
the basic chemical principles behind the Stewart approach dictate that it is the ECF composition which determines the plasma pH.
consult the glossary for other aspects of acid-base equilibria and the rules and mathematics behind our website: