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# Total inorganic carbon

The total inorganic carbon (CT, 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 anion. It is customary to express carbon dioxide and carbonic acid simultaneously as CO2* . CT is an important parameter when making measurements related to the pH of natural aqueous systems, and carbon dioxide flux estimates.

CT = [CO2*] + [HCO3] + [CO32−]

where,

• CT is the total inorganic carbon
• [CO2*] is the sum of carbon dioxide and carbonic acid concentrations ( [CO2*] = [CO2] + [H2CO3])
• [HCO3] is the bicarbonate concentration
• [CO32−] is the carbonate concentration

Each of these species are intimately related by the following pH driven chemical equilibria:

CO2 + H2O $\rightleftarrows$ H2CO3 $\rightleftarrows$ H+ + HCO3 $\rightleftarrows$ 2H+ + CO32−

Total inorganic carbon is 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, typically by infrared spectroscopy.