Borgmann Aquaponics Hydroponics
Zinc occurs in nutrient solutions mainly as zinc ion (Zn²⁺) .
There are different methods for determining zinc:
- Atomic absorption spectroscopy (AAS): High-precision determination of zinc.
- Complexometric titration with EDTA: formation of a stable Zn-EDTA complex.
- Spectrophotometry with dithizone: color development by complex formation.
Detailed titration of zinc with EDTA
1. Principle of the method
Zinc ions (Zn²⁺) react with ethylenediaminetetraacetic acid (EDTA, C₁₀H₁₆N₂O₈) to form a stable complex:
The endpoint of the titration is detected using the Eriochrome Black-T (ErioT) indicator . The color changes from wine red to blue .
2. Chemicals
- 0.01 mol/L EDTA solution (C₁₀H₁₆N₂O₈)
- Buffer solution (pH 10, NH₃/NH₄⁺ buffer)
- Eriochrome Black-T (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 10).
- Add 2-3 drops of Eriochrome Black-T indicator.
- Titrate with 0.01 mol/L EDTA until the color changes from wine red to blue.
5. Calculation of zinc concentration
The concentration of Zn is calculated using the formula:
6. Example calculation:
- EDTA concentration: 0.01 mol/L
- Consumed volume: 8.5 mL (0.0085 L)
- Sample volume: 50 mL (0.050 L)
Conclusion
Complexometric titration with EDTA is a precise method for the quantitative determination of zinc in nutrient solutions.
The quantitativelyeDetermination of zincin hydroponic nutrient solutions requires special care in sampling and sample preparation, as zincone of the most common contamination elements in analytical practice. Even the smallest entries from vascular materials, reagents or laboratory air can significantly distort the measurement results, especially since the optimal zinc-Concentrations in hydroponic solutions are relatively low at 0.3 to 1.5 mg/l. The most established method for precise zinc-Analyses are the flame AAS at 213.9 nm, which provides optimal sensitivity for this concentration range and minimizes matrix effects by using deuterium-based subsurface correction methods. In practical hydroponic monitoring, photometric methods are also used, which are based on the formation of colored zinc-Based complexes with dithizone or zincone. A critical aspect of the zinc-Analytics is the distinction between dissolved and particulate bound zinc, since precipitates are zinchydroxide or zincphosphate at pH values above 7.0 can drastically reduce bioavailability without decreasing the overall concentration. For meaningful process control, the filtered measured zinc-Concentration can be used as a measure of actual availability. The interpretation of the analysis results must also take into account the antagonistic relationship to iron and copper, since increased zinc-Concentrations can block the uptake of these trace
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