Nickel occurs in nutrient solutions mainly as nickel ion (Ni²⁺) .

There are various methods for determining nickel:

• Atomic absorption spectroscopy (AAS): High-precision determination of nickel.
• Complexometric titration with EDTA: Formation of a stable Ni-EDTA complex.
• Spectrophotometry with dimethylglyoxime (DMG): color development by complex formation.

Detailed titration of nickel with EDTA

1. Principle of the method

Nickel ions (Ni²⁺) react with ethylenediaminetetraacetic acid (EDTA, C₁₀H₁₆N₂O₈) to form a stable complex:

The endpoint of the titration is detected using the murexide indicator . The color change occurs from violet to yellow-orange .

2. Chemicals

• 0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
• Buffer solution (pH 9-10, NH₃/NH₄⁺ buffer)
• Murexide (indicator)

3. Experimental setup

Required equipment:

• Burette (25 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 10 mL of buffer solution (pH 9-10).
3. Add 2-3 drops of murexide indicator.
4. Titrate with 0.01 mol/L EDTA until the color changes from violet to yellow-orange.

5. Calculation of nickel concentration

The concentration of Ni is calculated using the 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)
  $c\left(\mathrm{Ni}\right)=\frac{0.0124\cdot 0.01\cdot 1}{1\cdot 0.050}=0.00248\text{mol/L}=2.48\text{mmol/L}$