Bicarbonate is present if the alkalinity to phenolphthalein is less than
one-half the alkalinity to methyl orange, erythrosine, or lacmoid. The
alkalinity to methyl orange, erythrosine, or lacmoid is due entirely to
bicarbonate if there is no phenolphthalein alkalinity. If there is
phenolphthalein alkalinity the bicarbonate, in terms of calcium
carbonate, is equal to the methyl orange, erythrosine, or lacmoid
alkalinity minus twice the phenolphthalein alkalinity. Bicarbonate,
carbon dioxide as bicarbonate, and half-bound carbon dioxide can be
calculated as follows:
Bicarbonate (HCO_{3}) = 1.22 times the bicarbonate expressed in terms of
calcium carbonate.
Carbon dioxide (CO_{2}) as bicarbonate = 0.88 times the bicarbonate
expressed in terms of calcium carbonate.
Half-bound carbon dioxide (CO_{2}) = 0.44 times the bicarbonate
expressed in terms of calcium carbonate.