Complexometric Titration
Introduction
• A titration method based on the formation of a stable complex between a metal ion and a complexing agent (ligand).
• Commonly used for determining metal ions in solution.
• EDTA (Ethylenediaminetetraacetic acid) is the most widely used complexing agent.
Principle
• A metal ion (Mn⁺) reacts with a ligand (L) to form a stable complex:
Mn+ + L ⇌ MLn
• The reaction is monitored using an appropriate indicator or instrumental method.
Types of Complexometric Titrations
1. Direct Titration: Metal ion is titrated directly with EDTA.
2. Back Titration: Excess EDTA is added to metal ion, then the remaining EDTA is titrated with a standard metal ion solution.
3. Replacement Titration: A weakly bound metal complex is displaced by a stronger one and titrated.
4. Indirect Titration: Used for anions that form precipitates with metal ions (e.g., sulfate determination via Ba²⁺).
Indicators Used
• Metal ion indicators (e.g., Eriochrome Black T for Ca²⁺ and Mg²⁺)
• Indicators change color at the endpoint due to the metal-ligand interaction.
Applications
• Water hardness determination (Ca²⁺ and Mg²⁺).
• Estimation of metal ions in pharmaceuticals.
• Analysis of industrial effluents.
• Determination of metal impurities in food and beverages.
Advantages
• Highly specific and sensitive.
• Can determine multiple metal ions in a single solution.
• Requires simple apparatus and reagents.
Limitations
• Requires stable metal-ligand complex formation.
• Proper pH control is necessary for accurate results.
• Some metal ions may require masking agents to prevent interference.
Complexometric Titration
Introduction
• A titration method based on the formation of a stable complex between a metal ion and a complexing agent (ligand).
• Commonly used for determining metal ions in solution.
• EDTA (Ethylenediaminetetraacetic acid) is the most widely used complexing agent.
Principle
• A metal ion (Mn⁺) reacts with a ligand (L) to form a stable complex:
Mn+ + L ⇌ MLn
• The reaction is monitored using an appropriate indicator or instrumental method.
Types of Complexometric Titrations
1. Direct Titration: Metal ion is titrated directly with EDTA.
2. Back Titration: Excess EDTA is added to metal ion, then the remaining EDTA is titrated with a standard metal ion solution.
3. Replacement Titration: A weakly bound metal complex is displaced by a stronger one and titrated.
4. Indirect Titration: Used for anions that form precipitates with metal ions (e.g., sulfate determination via Ba²⁺).
Indicators Used
• Metal ion indicators (e.g., Eriochrome Black T for Ca²⁺ and Mg²⁺)
• Indicators change color at the endpoint due to the metal-ligand interaction.
Applications
• Water hardness determination (Ca²⁺ and Mg²⁺).
• Estimation of metal ions in pharmaceuticals.
• Analysis of industrial effluents.
• Determination of metal impurities in food and beverages.
Advantages
• Highly specific and sensitive.
• Can determine multiple metal ions in a single solution.
• Requires simple apparatus and reagents.
Limitations
• Requires stable metal-ligand complex formation.
• Proper pH control is necessary for accurate results.
• Some metal ions may require masking agents to prevent interference.