Alkalinity measurement: Part 2 - A 4 pH point titration method to determine the carbonate weak acid/base in aqueous solutions containing other weak acid/bases of known concentrations

In this paper the 4 pH point titration method (see Part 1) is extended to determine the carbonate total species concentration (CT) and H 2 CO 3 * alkalinity in aqueous solutions containing other weak acid/bases of known concentrations. Two typical other weak acid/bases are selected, ammonium with a pK a far from, and inorganic phosphate with a pK a near to, the 4 pH point titration range of 7,2 to 4,8. The influence of the phosphate and ammonium on the 4 pH point titration is examined theoretically and experimentally. Knowing the total species concentrations of the ammonium and phosphate, their respective effects on the 4 pH point titration are assessed and corrected for, to isolate C T and H 2 CO 3 * alkalinity. With regard to the effect of ammonium, this is negligible for most practical applications of the 4 pH point titration and normally requires no correction