Hach DR/700 Procedures Manual page 576

CYANIDE,
continued
c) Add Sodium Arsenite Solution drop-wise until the sample turns
colorless. Swirl the sample thoroughly after each drop. Count the
number of drops.
d) Take another 25-mL sample and add the total number of drops of
Hydrochloric Acid Standard Solution counted in Step a.
e) Subtract one drop from the amount of Sodium Arsenite Solution
added in Step c. Add this amount to the sample and mix thoroughly.
f) Continue with Step 2 of the cyanide procedure.
Reducing Agents
a) Adjust a 25-mL portion of the alkaline sample to pH 7-9 with 2.5 N
Hydrochloric Acid Standard Solution. Count the number of drops
added.
b) Add 4 drops of Potassium Iodide Solution and 4 drops of Starch
Indicator Solution to the sample. Swirl to mix. The sample should be
colorless.
c) Add Bromine Water drop-wise until a blue color appears. Swirl the
sample thoroughly after each addition. Count the number of drops.
d) Take another 25 mL sample and add the total number of drops of
Hydrochloric Acid Standard Solution counted in Step a.
e) Add the total number of drops of Bromine Water counted in Step c to
the sample and mix thoroughly.
f) Continue with Step 2 of the cyanide procedure.
Metals
Nickel or cobalt in concentrations up to 1 mg/L do not interfere.
Eliminate the interference from up to 20 mg/L copper and 5 mg/L iron
by adding the contents of one HexaVer Chelating Reagent Powder
Pillow to 25 mL of sample and then mixing before adding the CyaniVer
3 Cyanide Reagent powder Pillow in Step 2. Prepare a reagent blank of
demineralized water and CyaniVer 3, CyaniVer 4, CyaniVer 5 reagent
and HexaVer Chelating reagent to zero the instrument in Step 15.
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