How can a sample containing oxidizers be pretreated for cyanide testing?

Document ID

Document ID TE1215

Published Date

Published Date 05/25/2022
Question
How can a sample containing oxidizers be pretreated for cyanide testing?
Summary
Treating cyanide samples for oxidizers
Answer
Oxidizing agents such as chlorine decompose cyanides during storage. To test for and remove oxidizing agents, pretreat the sample as instructed in US ENG Cyanide, Pyridine-Pyrazalone Method 8027, Powder Pillows_DOC316.53.01040(same as what follows):
 
  1. Measure 25 mL of the sample and add one drop of 10 g/L m-Nitrophenol Indicator Solution. Swirl to mix.
  2. Add 2.5 N Hydrochloric Acid Standard Solution by drops until the color changes from yellow to colorless. Swirl the sample thoroughly after the addition of each drop.
  3. Add two drops of Potassium Iodide Solution, 30 g/L and two drops of Starch Indicator Solution to the sample. Swirl to mix. The solution will turn blue if oxidizing agents are present.
  4. If the color is blue, add two level 1g scoops of ascorbic acid per liter of sample.
  5. Remove a 25 mL portion of the treated sample and repeat steps 1 to 3. If the sample turns blue, repeat steps 4 and 5.
  6. If the 25 mL sample remains colorless, preserve the remaining sample to pH 12 for storage with 5 N Sodium Hydroxide Standard Solution.
  7. Complete the procedure given under Interfering Substances and Levels, Reducing Agents, in Method 8027 to eliminate the effect of exess ascorbic acid, before the cyanide procedure is started.

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