Calcium ion detection method?
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Could you provide more details on the methods for detecting the calcium ion content in kaolin, molecular sieves, and similar materials? We tried several criteria, but the color changes of the indicators listed there were not noticeable. Are there any good indicators? Have used CMP indicator, Eriochrome Black T
It’s likely interference from high-valent ions such as iron, copper, and aluminum; try using a high concentration of triethanolamine as a shield.
Transfer 50 ml of the test solution into a 500 ml conical flask, add 10 ml of the triethanolamine-sodium potassium tartrate mixture, and 1 drop of bromothymol blue indicator (5 g/L). Neutralize with ammonia solution (1+1) until the solution turns blue. Add exactly 0.5 ml of copper sulfate-EDTA solution, then add 8 ml of ammonia solution (1+1) and 3 drops of PAR indicator (1 g/L). Titrate with an EDTA standard solution at a concentration of 0.01961 mol/L until the color of the solution changes from purplish-red to purplish-gray and then to green, at which point the titration is complete.
There are many metal elements inside; it is recommended to add a shielding agent before conducting titration tests
Generally, a calcium carboxylate indicator or Eriochrome Black T is used; at a pH of 12, 2 mL of triethanolamine in a 1:1 ratio is added to mask ions such as iron and aluminum. The endpoint is reached when the color changes from blue to burgundy, which is quite noticeable.