Boron, quantitative analysis

Quantitative Analyse von Bor

Boron is present in nutrient solutions mainly as borate species (B(OH)₄⁻) .

There are various methods for determining boron:

  • Spectrophotometry with azomethine-H: color development by complex formation.
  • ICP-OES (Inductively Coupled Plasma with Optical Emission): High-precision determination.
  • Manual titration with mannitol and NaOH: formation of a stable boron-mannitol complex.

Detailed titration of boron with mannitol and sodium hydroxide

1. Principle of the method

Boron forms a stable bormannitol complex with mannitol , which can be titrated as a strong acid:

B(OH)3 + Mannitol → Bormannitol-Komplex

The complex can then be titrated with sodium hydroxide (NaOH) .

2. Chemicals

  • 0.01 mol/L sodium hydroxide solution (NaOH)
  • Mannitol (C₆H₁₄O₆, as a reagent)
  • Phenolphthalein (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 5 g of mannitol and dissolve.
  3. Add 2-3 drops of phenolphthalein indicator.
  4. Titrate with 0.01 mol/L NaOH until the color changes from colorless to pink.

5. Calculation of the boron concentration

The concentration of B is calculated using the formula:

c ( B ) = V NaOH ⋅ c NaOH ⋅ 1 1 V Probe

 

6. Example calculation:

  • NaOH concentration: 0.01 mol/L
  • Consumed volume: 6.3 mL (0.0063 L)
  • Sample volume: 50 mL (0.050 L)
c ( B ) = 0.0063 ⋅ 0.01 ⋅ 1 1 ⋅ 0.050 = 0.00126 mol/L = 1.26 mmol/L

 

Conclusion

Titration with mannitol and NaOH is a simple procedure.

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ID: 628 

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Parent Category: Technology
Category: Analysis
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Analysis