The main compounds of alkalinity are: hydroxides (OH-), carbonates (CO32-), and bicarbonates (HCO3-).  The alkalinity, or buffering capacity, of a solution depends on the absorption of positively charged hydrogen ions by negatively charged bicarbonate and carbonate molecules.  When bicarbonate and carbonate molecules absorb hydrogen ions, there is a shift in equilibrium without a significant shift in pH.  A sample with high buffering capacity will have high bicarbonate and/or carbonate content, and a greater resistance to changes in pH.  For more information on MANTECH’s method for automated alkalinity measurement and how the species of alkalinity are calculated, download the pdf.