Iron is usually present in nutrient solutions as Fe²⁺ (e.g., in chelates) or Fe³⁺ (free iron). The following methods are used for determination:

• Complexometric titration with EDTA: Frequently used method for Fe³⁺.
• Spectrophotometry with phenanthroline: For Fe²⁺.
• Atomic absorption spectroscopy (AAS): High-precision laboratory analysis.
• ICP-OES: Accurate for multiple measurements, but complex.

Detailed titration of iron with EDTA

1. Principle of the method

Iron(III) ions ( Fe³⁺ ) form a stable chelate complex with EDTA (C₁₀H₁₆N₂O₈) :

Endpoint detection is carried out using the indicator xylenol orange , which changes from red to yellow.

2. Chemicals

• 0.01 mol/L EDTA solution
• Xylenol orange (indicator)
• Acetic acid/sodium acetate buffer solution (pH 5-6)
• 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

1. Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
2. Add 5 mL of acetate buffer solution (pH 5-6).
3. Add 2-3 drops of xylenol orange as an indicator (color: red).
4. Titrate with 0.01 mol/L EDTA solution until the color changes from red to yellow.

5. Calculation of iron concentration

The iron concentration is calculated using the following formula:

6. Example calculation:

• EDTA concentration: 0.01 mol/L
• Consumed volume: 12.4 mL (0.0124 L)
• Sample volume: 50 mL (0.050 L)

Comparison of methods