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D2180-17 – Standard Test Method Technical Guide
📐 Test Method Scope and Summary
This test method covers the determination of inorganic “active oxygen” in bleaching compounds such as perborates, percarbonates, and peroxides. It specifically excludes persulfates and monopersulfates. Active oxygen is defined as the measure of oxidizing power, expressed in terms of oxygen (O) with a gram-equivalent weight of 8.00. The summary of the test method involves titrating an acidified aqueous solution of the compound with a standard solution of potassium permanganate.
Note: The use of a molybdate-catalyzed iodometric method has been suggested, but the permanganate method is preferred to minimize reactions with organic constituents.
⚙️ Reagents and Procedure
All reagents must be of reagent grade, conforming to ACS specifications where available. Water must comply with Specification D1193. The standard potassium permanganate solution (0.1 N) is prepared by dissolving 3.2 g of KMnO₄ in 100 mL of water and diluting to 1 L. The solution is allowed to stand in the dark for two weeks to stabilize, then filtered through a fine-porosity sintered-glass crucible. It should be stored in glass-stoppered, amber-colored bottles to avoid photodegradation.
The solution is standardized using sodium oxalate (Na₂C₂O₄) previously dried at 105°C. Weigh accurately to the nearest 0.1 mg.
| 🟦 Component | 📏 Quantity | 🎯 Procedure |
|---|---|---|
| Potassium Permanganate (KMnO₄) | 3.2 g | Dissolve in 100 mL water, dilute to 1 L, stand 2 weeks in dark, filter through sintered-glass crucible |
| Sodium Oxalate (Na₂C₂O₄) | 0.3 g | Dry at 105°C, weigh accurately to 0.1 mg for standardization |
📊 Interferences and Considerations
Interference from organic constituents must be carefully evaluated. A sluggish titration or vague end point may indicate organic interference. Inorganic builders such as silicates, phosphates, and carbonates do not interfere. However, organic detergents, wetting agents, and EDTA-type sequestrants can interfere. It is recommended to use the permanganate method with minimal excess of titrant to avoid side reactions.
⚠️ Safety Data Sheets (formerly Material Safety Data Sheets) are available for reagents and materials. Review them for hazards prior to usage. Appropriate safety and health practices must be established.
💡 Do not permit the filtered potassium permanganate solution to come into contact with paper, rubber, or other organic material. Store in glass-stoppered, amber-colored glass bottles to ensure stability.
❓ Frequently Asked Questions
🔍 What is active oxygen and how is it measured?
Active oxygen is the oxidizing power of compounds like perborates and peroxides, expressed as oxygen (O) with equivalent weight 8.00. It is measured by titrating an acidified solution with potassium permanganate.
💡 Why is potassium permanganate used instead of iodometric methods?
The permanganate method minimizes reactions with organic constituents, unlike iodometric methods where liberated iodine may react with organics. Titration is performed to avoid excess permanganate.
⚡ What substances can interfere with the test?
Organic constituents, detergents, wetting agents, and EDTA-type sequestrants can interfere. Inorganic builders like silicates, phosphates, and carbonates do not interfere. A sluggish reaction suggests interference.
📌 How should the potassium permanganate solution be prepared and stored?
Dissolve 3.2 g KMnO₄ in 100 mL water, dilute to 1 L, stand in dark for 2 weeks, filter through sintered-glass crucible. Store in amber-colored glass bottles away from organic materials.