The inorganic carbon species include carbon dioxide, carbonic acid, bicarbonate anion, and carbonate.    It is customary to express carbon dioxide and carbonic acid simultaneously as . C is a key parameter when making measurements related to the pH of natural aqueous systems, and carbon dioxide flux estimates.
where,
* C is the total inorganic carbon
*  is the sum of carbon dioxide and carbonic acid concentrations  ()
*  is the bicarbonate concentration
*  is the carbonate concentration
Each of these species are related by the following pH-driven chemical equilibria:
The concentrations of the different species of DIC (and which species is dominant) depends on the pH of the solution, as shown by a Bjerrum plot.
Total inorganic carbon is typically measured by the acidification of the sample which drives the equilibria to .  This gas is then sparged from solution and trapped, and the quantity trapped is then measured, usually by infrared spectroscopy.