Borgmann Aquaponics Hydroponics
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
- Pour 10 mL of the nutrient solution into a 250 mL Erlenmeyer flask.
- Add 10 mL of buffer solution (pH 9-10).
- Add 2-3 drops of murexide indicator.
- 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)
Addition:
- If other indicators (e.g. xylene orange) are used, the color change is red → yellow .
- The method works optimally at pH 9–10 , but higher pH values (>10) should be avoided because nickel hydroxide (Ni(OH)₂) may precipitate.
Conclusion
Complexometric titration with EDTA is a precise method for the quantitative determination of nickel in nutrient solutions.
Nickel analysis in hydroponic systems presents unique challenges due to the extremely low concentrations required for plant nutrition, typically between 0.05 and 0.5 mg/l, as nickel serves as an essential cofactor for the urease enzyme responsible for nitrogen metabolism. For reliable quantification at these ultra-trace levels, graphite furnace atomic absorption spectrometry (GF-AAS) or inductively coupled plasma mass spectrometry (ICP-MS) are the preferred methods, offering detection limits in the ng/l range that conventional flame AAS cannot achieve. Sample preparation requires particular attention to avoid contamination from stainless steel equipment, which can leach significant nickel amounts during acidification. In hydroponic practice, nickel deficiency is rarely observed but becomes critical in recirculating systems using reverse osmosis water and purified fertilizers, where unintended nickel inputs are minimized. The analytical results gain additional significance when troubleshooting urea-based fertilization regimes, as insufficient nickel directly impairs urea hydrolysis and leads to ammonium toxicity symptoms despite adequate nitrogen supply. Recent research has also highlighted nickel's role in mitigating oxidative stress, suggesting that maintaining optimal nickel concentrations may enhance crop resilience under suboptimal growing conditions.
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