Summary of Method

The total organic carbon (TOC) is determined by first sparging the sample under slightly
acidic conditions to remove the inorganic carbon. In the outside vial, organic carbon in the
sample is digested by persulfate and acid to form carbon dioxide. During digestion, the
carbon dioxide diffuses into a pH indicator reagent in the inner ampule. The adsorption of
carbon dioxide into the indicator forms carbonic acid. Carbonic acid changes the pH of the
indicator solution which, in turn, changes the color. The amount of color change is related to
the original amount of carbon present in the sample. Test results are measured at 598 and
430 nm.

DOC is filtered through a 0.45 um membrane filter.

Method 10128 Direct Method HR (100 to 700 mg/L C)
Method 10129 Direct Method LR (0.3 to 20.0 mg/L C)
Method 10173 Direct Method MR (15 to 150 mg/L C)

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