Copper can occur in nutrient solutions in various forms, such as:

• Free copper ion (Cu²⁺) – directly available to plants.
• Complexed copper – bound to chelates such as EDTA.

There are several methods for determining copper:

• Spectrophotometry: Color development with neocuproine or bicinchoninic acid.
• Atomic absorption spectroscopy (AAS): High-precision method for trace analysis.
• Complexometric titration with EDTA: Suitable for direct Cu²⁺ determination.

Detailed titration of copper with EDTA

1. Principle of the method

During the titration, Copper (Cu²⁺) is complexed with Ethylenediaminetetraacetate (EDTA) in a basic medium: 

The reaction is carried out at pH = 10 to exclude other metals (e.g. Ca²⁺).

2. Chemicals

• EDTA solution (0.05 mol/L)
• Ammonia buffer solution (pH = 10)
• Indicator: Murexide (color change from yellow → violet)

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 murexide indicator (solution turns yellow).
4. Titrate with 0.05 mol/L EDTA until the color changes to violet.

5. Calculation of copper concentration

The concentration of Cu²⁺ is calculated using the formula:

6. Example calculation:

• EDTA concentration: 0.05 mol/L
• Consumed volume: 9.4 mL (0.0094 L)
• Sample volume: 50 mL (0.050 L)