Borgmann Aquaponics Hydroponics
Cobalt occurs in nutrient solutions primarily as the cobalt(II) ion (Co²⁺) . Required by rhizobia, it is important for the nodulation of legumes. A non-essential micronutrient.
There are various methods for determining cobalt:
- Atomic absorption spectroscopy (AAS): High-precision determination of cobalt.
- Spectrophotometry with nitroso-R salt: formation of a colored cobalt complex.
- Complexometric titration with EDTA: Formation of a stable cobalt-EDTA complex.
Detailed titration of cobalt with EDTA
1. Principle of the method
Cobalt ions (Co²⁺) react with ethylenediaminetetraacetic acid (EDTA, C₁₀H₁₆N₂O₈) to form a stable complex:
The endpoint of the titration is detected using Eriochrome Black-T (ErioT) as an indicator. The color change occurs from **pink 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 pink to blue.
5. Calculation of the cobalt concentration
The concentration of Co is calculated using the formula:
6. Example calculation:
- EDTA concentration: 0.01 mol/L
- Consumed volume: 9.2 mL (0.0092 L)
- Sample volume: 50 mL (0.050 L)
Complexometric titration with EDTA is a precise method for the quantitative determination of cobalt in nutrient solutions.
In hydroponic systems, cobalt analysis is critical due to its dual role as an essential component for nitrogen fixation in legumes and as a potential toxicant at elevated concentrations. For French bean (Phaseolus vulgaris), toxicity thresholds have been established at 26 μg g⁻¹ dry weight in young leaves for the onset of symptoms, with acute toxicity occurring at 72 μg g⁻¹. Excess cobalt (>0.0001 mM) decreases chlorophyll concentration, Hill reaction activity, and catalase activity while increasing phenols and peroxidase activity. For chickpea, 50 μM cobalt represents a threshold concentration that significantly increases nodule number, leghemoglobin concentration, and nitrogenase activity, whereas concentrations above 100 μM become inhibitory. Analytical methods must achieve detection limits below 0.1 mg/L in nutrient solutions, with graphite furnace AAS or ICP-MS recommended for precise quantification. Sample preservation requires acidification to pH <2 to prevent cobalt adsorption to container walls. Regular monitoring is essential as cobalt interferes with iron uptake, with increasing cobalt supply concomitantly decreasing iron concentrations in plant tissues.
Quellen: Chatterjee, C., & Chatterjee, M. (2000). Phytotoxicity of cobalt, chromium and copper in cauliflower. Chatragadda, R. (2020). Cobalt and molybdenum co-catalysis for enhanced nitrogen fixation in chickpea.
Add Comment