If the pH the sample is less than 8.3, the alkalinity is all in the form of bicarbonate. Samples containing carbonate and bicarbonate alkalinity have a pH greater than 8.3, and titration to the phenolphthalein end point represents ½ of the carbonate alkalinity, conversion to HCO3-. If the millilitres of phenolphthalein titrant equals the millilitres of methyl orange titrant, all of the alkalinity is in the form of carbonate. Any alkalinity in excess of this amount is due to hydroxide.