Hach DR/850 Procedures Manual page 304

ORGANIC CARBON, TOTAL, Mid Range,
Note: If the sample contains greater than 1000 mg/L CaCO
testing by adding sulfuric acid solution.
Note: Most sample turbidity is either dissolved during the digestion stage or settled during the cooling period.
Sample turbidities up to 50 NTU have been tested without interference.
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.
Table 1 Non-interfering Substances (Continued)
Substance
Monochloramine
Nitrite
Ozone
Phosphate
Silica
Sulfate
Sulfide
Sulfite
Zinc
3
304
continued
Maximum Level Tested
14 mg/L NH
500 mg/L NO
2 mg/L O
3390 mg/L PO
100 mg/L SiO
5000 mg/L SO
20 mg/L S
50 mg/L SO
5 mg/L
alkalinity, lower the sample pH to less than 7 before
Cl as Cl
2 2
-
2
3
3-
4
2
2-
4
2-
2-
3