What are the common problems in measuring calcium in feed?
Problems in measuring calcium in feed
Determination of the test sample
Accurately pipette 10 mL to 20 mL of the sample solution (containing about 20 mg of calcium) into a 200 mL beaker, add 100 mL of distilled water and 2 drops of methyl red indicator (4.8), then add ammonia solution (4.5) dropwise until the solution turns orange. If too much is added, add hydrochloric acid solution (4.3) to adjust it back to orange, then add 2 more drops to make it pink (pH 2.5-3.0). Carefully boil, then slowly add 10 mL of hot ammonium oxalate solution (4.6) dropwise while stirring constantly. If the solution turns orange, add more hydrochloric acid solution (4.3) to make it red. Boil for several minutes and leave to stand overnight so the precipitate ages (or heat in a water bath for 2 h). What is the purpose of adding ammonia solution and hydrochloric acid in the determination procedure? Why not add ammonium oxalate directly after methyl red to form the calcium oxalate precipitate? And then titrate with potassium permanganate in an acidic environment?
Accurately pipette 10 mL to 20 mL of the sample solution (containing about 20 mg of calcium) into a 200 mL beaker, add 100 mL of distilled water and 2 drops of methyl red indicator (4.8), then add ammonia solution (4.5) dropwise until the solution turns orange. If too much is added, add hydrochloric acid solution (4.3) to adjust it back to orange, then add 2 more drops to make it pink (pH 2.5-3.0). Carefully boil, then slowly add 10 mL of hot ammonium oxalate solution (4.6) dropwise while stirring constantly. If the solution turns orange, add more hydrochloric acid solution (4.3) to make it red. Boil for several minutes and leave to stand overnight so the precipitate ages (or heat in a water bath for 2 h). What is the purpose of adding ammonia solution and hydrochloric acid in the determination procedure? Why not add ammonium oxalate directly after methyl red to form the calcium oxalate precipitate? And then titrate with potassium permanganate in an acidic environment?