ASTM D5904-02(2017)

1.1 This test method covers the determination of total carbon (TC), inorganic carbon (IC), and total organic carbon (TOC) in water in the range from 0.5 to 30 mg/L of carbon. Higher levels may be determined by sample dilution. The test method utilizes ultraviolet-persulfate oxidation of organic carbon, coupled with a CO₂ selective membrane to recover the CO₂ into deionized water. The change in conductivity of the deionized water is measured and related to carbon concentration in the oxidized sample. Inorganic carbon is determined in a similar manner without the requirement for oxidation. In both cases, the sample is acidified to facilitate CO₂ recovery through the membrane. The relationship between the conductivity measurement and carbon concentration is described by a set of chemometric equations for the chemical equilibrium of CO₂, HCO₃⁻, H⁺, and the relationship between the ionic concentrations and the conductivity. The chemometric model includes the temperature dependence of the equilibrium constants and the specific conductances.