After precipitation or color method, which chelating agent is commonly used to separate calcium from dyes and reach endpoint color?

After precipitation or color method, which chelating agent is commonly used to separate calcium from dyes and reach endpoint color?

• A. EDTA
• B. EGTA
• C. DTPA
• D. NTA

Answer: (A)

In this setup, the goal is to pull calcium away from the dye complex so the indicator’s color can clearly change at the endpoint. EDTA binds calcium very strongly, forming a stable calcium–EDTA complex. When you add EDTA during the titration, it sequesters Ca2+ from the dye–Ca complex, and the indicator shifts to its endpoint color as the calcium is fully chelated. This produces a sharp, easily readable end point, which is why EDTA is the standard choice for calcium determinations in complexometric titrations. Other chelators exist but are less commonly used for routine calcium dye methods because of differences in affinity, selectivity, or practicality.

In this setup, the goal is to pull calcium away from the dye complex so the indicator’s color can clearly change at the endpoint. EDTA binds calcium very strongly, forming a stable calcium–EDTA complex. When you add EDTA during the titration, it sequesters Ca2+ from the dye–Ca complex, and the indicator shifts to its endpoint color as the calcium is fully chelated. This produces a sharp, easily readable end point, which is why EDTA is the standard choice for calcium determinations in complexometric titrations. Other chelators exist but are less commonly used for routine calcium dye methods because of differences in affinity, selectivity, or practicality.