Calcium occurs in nutrient solutions mostly as Ca²⁺ ion and can be determined using various methods:
- Complexometric titration with EDTA: Frequently used method.
- Atomic absorption spectroscopy (AAS): Very precise but expensive laboratory analysis.
- ICP-OES (Inductively Coupled Plasma with Optical Emission): High-precision method for multiple measurements.
Detailed titration of calcium with EDTA
1. Principle of the method
Calcium ions (Ca²⁺) react with ethylenediaminetetraacetic acid (EDTA, C₁₀H₁₆N₂O₈) to form a stable chelate complex:
The endpoint is detected using the Eriochrome Black T (indicator) , which changes from red to blue.
2. Chemicals
- 0.01 mol/L EDTA solution
- Eriochrome Black-T (indicator)
- Ammonia buffer solution (pH 10)
- Distilled water
3. Experimental setup
Required equipment:
- Burette (50 mL, division 0.1 mL)
- Erlenmeyer flask (250 mL)
- Pipette (10 mL)
- Magnetic stirrer
4. Implementation
- Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
- Add 5 mL of ammonia buffer solution (pH 10).
- Add 2-3 drops of Eriochrome Black-T as an indicator (color: red).
- Titrate with 0.01 mol/L EDTA solution until the color changes from red to blue .
5. Calculating the calcium concentration
The calcium concentration is calculated using the following formula:
6. Example calculation:
- EDTA concentration: 0.01 mol/L
- Consumed volume: 8.5 mL (0.0085 L)
- Sample volume: 50 mL (0.050 L)
Conclusion
Titration with EDTA is a reliable and cost-effective method for determining calcium in nutrient solutions.
ID: 627
Kontext:
