Total Inorganic Carbon

The total inorganic carbon (C_T, or TIC) or dissolved inorganic carbon (DIC) is the sum of inorganic carbon species in a solution. 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 CO₂* . C_T is an key parameter when making measurements related to the pH of natural aqueous systems, and carbon dioxide flux estimates.

C_T = + +

where,

• C_T 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:

CO₂ + H₂O H₂CO₃ H+ + HCO₃− 2H+ + CO₃2−

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 CO₂. This gas is then sparged from solution and trapped, and the quantity trapped is then measured, usually by infrared spectroscopy.