Hach DR/850, Procedures Manual, Page: 312 / 460

312
ORGANIC CARBON, TOTAL, High Range,
continued
If the sample contains greater than 600 mg/L CaCO
3
alkalinity,
lower the sample pH to less than 7 before testing by adding
sulfuric acid solution.
Most sample turbidity is either dissolved during the digestion
stage or settled during the cooling period. Sample turbidities up
to 900 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.
REQUIRED REAGENTS
Total Organic Carbon Direct Method High Range
Test ’N Tube Reagent Set................................................................50 vials.......... 27604-45
Includes:
Description Qty/Test Unit Cat. No.
Acid Digestion Solution Vials, High Range TOC .................. 1 ............. 50/pkg
............................. *
Buffer Solution, Sulfate ..................................................... 0.4 mL .........25 mL.............. 452-33
Funnel, micro .......................................................................... 1 ................. each.......... 25843-35
Indicator Ampules, High Range TOC .................................... 1 ............. 10/pkg....................... *
TOC Persulfate Powder Pillows ............................................. 1 ............. 50/pkg....................... *
Water, organic-free
**
......................................................... 0.3 mL .......500 mL.......... 26415-49
Silica 100 mg/L SiO
2
Sulfate 5000 mg/L SO
4
2-
Sulfide 20 mg/L S
2-
Sulfite 50 mg/L SO
3
2-
Zinc 5 mg/L
Table 1 Non-interfering Substances (Continued)
Substance Maximum Level Tested
* These items are not sold separately.