Hach DR/850, Руководство по процедурам, Страница: 296 / 460

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ORGANIC CARBON, TOTAL, Low 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 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.
REQUIRED REAGENTS
Description Qty/Test Unit Cat. No.
Total Organic Carbon Direct Method Low Range
Test ’N Tube Reagent Set................................................................50 vials.......... 27603-45
Includes:
Acid Digestion Solution Vials, Low Range TOC................... 1 ............. 50/pkg
............................. *
Buffer Solution, Sulfate ..................................................... 0.4 mL .........25 mL.............. 452-33
Funnel, micro .......................................................................... 1 ................. each.......... 25843-35
Indicator Ampules, Low Range TOC ..................................... 1 ............. 10/pkg....................... *
TOC Persulfate Powder Pillows ............................................. 1 ............. 50/pkg....................... *
Water, organic-free
**
......................................................... 3.0 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.
** This item must be purchased separately.