Organic Carbon, Total
Organic Carbon, Total
OrganicCarbonTotal_Other_Low_DIR_Eng_Ody.fm Page 5 of 6
5. Continue the test starting at step 8 on page 2 of this procedure.
6. The mg/L C concentration should increase by 5.0 mg/L for each 0.1 mL
increment.
See Section 3.2.2 Standard Additions on page 32 for more information.
Standard Solutions Method
1. Prepare a 1000-mg/L organic carbon stock standard by dissolving 2.1254 g
dry primary standard Potassium Acid Phthalate in Organic-free Reagent
Water and dilute to 1000 mL. This stock standard is stable for about 1 month
at room temperature.
Alternatively, open one ampule of TOC Standard Solution
(Cat. No. 27915-05).
2. Prepare a 10.0-mg/L C standard by transferring 10.00 mL of the stock
standard to a 1000-mL Class A volumetric flask. Dilute to volume using
Organic-Free Reagent Water. Stopper and mix thoroughly. Prepare this
standard fresh daily.
Method Performance
Precision
See Section 3.4.3 Precision on page 44 for more information, or if the standard
concentration did not fall within the specified range.
Sensitivity
See Section 3.4.5 Sensitivity on page 44 Sensitivity for more information.
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.
Program mg/L C 95% Confidence Limits of Distribution
427 1 ±1.6 mg/L C
427 5 ±1.1 mg/L C
427 10 ±0.7 mg/L C
427 15 ±0.6 mg/L C
427 20 ±0.7 mg/L C
Portion of Curve ∆Abs ∆Concentration
Mid-range 0.010 0.3 mg/L C
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