Lithium occurs in nutrient solutions primarily as the lithium ion (Li+) . Li+ can increase the chlorophyll content of some plants (e.g., potato and pepper plants). A non-essential micronutrient.
There are different methods for determining lithium:
- Atomic absorption spectroscopy (AAS): High-precision method for determining lithium.
- Flame photometry: A simple and sensitive method for measuring lithium.
- Complexometric titration with EDTA: A less common method, but possible with selected indicators.
Detailed precipitation titration of lithium with ammonium tetraphenylborate
1. Principle of the method
Lithium ions (Li⁺) react with ammonium tetraphenylborate (NH₄BPh₄) and form a poorly soluble precipitate:
The end point of the titration is determined by turbidity or gravimetrically.
2. Chemicals
- 0.01 mol/L ammonium tetraphenylborate solution (NH₄BPh₄)
- Ethanol-water mixture as solvent
- Phenolphthalein as a turbidity 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 20 mL of ethanol-water mixture.
- Titrate with 0.01 mol/L ammonium tetraphenylborate solution until a permanent turbidity is visible .
5. Calculation of the lithium concentration
The concentration of lithium is calculated using the formula
:
6. Beispielrechnung:
- Ammoniumtetraphenylborat-Konzentration: 0,01 mol/L
- Verbrauchtes Volumen: 7,5 mL (0,0075 L)
- Probenvolumen: 50 mL (0,050 L)
Fazit
Die Fällungstitration mit Ammoniumtetraphenylborat ist eine zuverlässige Methode zur quantitativen Bestimmung von Lithium in Nährstofflösungen.
