Prepare Reagent A; Prepare Reagent B; Prepare Standard 0 - Hach CODmax III User Manual

3.3.1 Prepare reagent A

Chemical and inhalation hazard. Mercury sulfate is highly toxic. Exposure may result in
severe injury or death. Do not breathe mercury sulfate fumes. Use a fume hood to
prepare the solution.
Prepare potassium dichromate and mercury sulfate reagent (reagent A).
Items to collect:
• Sulfuric acid, 95–98%, ACS, 195 mL
• Potassium dichromate, PT, 80 g
• Mercury sulfate, ≥ 98.5%, ACS, 100 g
• Deionized water
1. Fill an applicable container with 1600 mL of deionized water.
2. Use a stirrer to mix.
3. Carefully add 80 g of potassium dichromate to the container.
4. Stir until the potassium dichromate is fully dissolved.
5. Carefully add 195 mL of sulfuric acid to the container.
6. Stir the solution. Let the solution temperature decrease to room temperature.
7. Carefully add 100 g of mercury sulfate to the container.
8. When mercury sulfate is fully dissolved, dilute to 2000 mL with deionized water.

3.3.2 Prepare reagent B

Prepare silver sulfate reagent (reagent B).
Items to collect:
• Sulfuric acid, 95–98%, ACS, 2000 mL
• Silver sulfate, ≥ 99.5%, ACS, 32 g
1. Add 32 g of silver sulfate to an applicable container.
2. Use a stirrer to mix.
3. Carefully add 2000 mL of sulfuric acid to the container. Stir until the silver sulfate is fully
dissolved.
Important: Do not add water to the solution.

3.3.3 Prepare standard 0

Prepare 0 mg/L standard solution (STD0).
Items to collect:
• Sulfuric acid, 95–98%, ACS, 1 mL
• Sodium sulfate, ≥ 99%, ACS, 0.1 g
• Deionized water
1. Add 800 mL of deionized water to an applicable container.
2. Use a stirrer to mix.
3. Carefully add 1 mL of sulfuric acid to the container.
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