Magnesium occurs in nutrient solutions as free magnesium ion (Mg²⁺) .

There are different methods for determining magnesium:

• Atomic absorption spectroscopy (AAS): High-precision determination of Mg²⁺.
• Complexometric titration with EDTA: Precise determination through the formation of stable chelate complexes.
• Flame photometry: Measurement of the emission of Mg²⁺ ions.

Detailed titration of magnesium with EDTA

1. Principle of the method

Magnesium ions (Mg²⁺) form a stable complex with Ethylenediaminetetraacetate (EDTA):

The titration is performed in the **pH range of 10** with ammonia buffer. Eriochrome Black T serves as an indicator, which changes from red to blue at the endpoint.

2. Chemicals

• 0.01 mol/L EDTA solution
• Ammonia buffer solution (pH = 10)
• Eriochrome Black T as indicator

3. Experimental setup

Required equipment:

• Burette (25 mL, division 0.1 mL)
• Erlenmeyer flask (100 mL)
• Pipette (10 mL)
• pH meter

4. Implementation

1. Pour 10 mL of the nutrient solution into a 100 mL Erlenmeyer flask.
2. Add 10 mL of ammonia buffer solution.
3. Add 3-5 drops of Eriochrome Black T (solution turns red).
4. Titrate with 0.01 mol/L EDTA until the color changes from red to blue.

5. Calculating the magnesium concentration

The concentration of Mg²⁺ is calculated using the formula:

6. Example calculation:

• EDTA concentration: 0.01 mol/L
• Consumed volume: 8.3 mL (0.0083 L)
• Sample volume: 50 mL (0.050 L)